Sync Source Changes :)

src/builder/java/speiger/src/builder/modules/MapModule.java

@@ -198,6 +198,7 @@ public class MapModule extends BaseModule
 		addBiRequirement("SortedMapNavigationTester");
 		addBiRequirement("OrderedMapNavigationTester");
 		addBiRequirement("OrderedMapMoveTester");
+		addBiRequirement("OrderedMapPutTester");
 		addBiRequirement("MapConstructorTester");
 		
 		addRemapper("TestMapGenerator", "Test%sMapGenerator");

src/builder/resources/speiger/assets/collections/templates/maps/impl/customHash/LinkedOpenCustomHashMap.template

@@ -713,6 +713,10 @@ public class LINKED_CUSTOM_HASH_MAP KEY_VALUE_GENERIC_TYPE extends CUSTOM_HASH_M
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<MAP.Entry KEY_VALUE_GENERIC_TYPE> implements ORDERED_MAP.FastOrderedSet KEY_VALUE_GENERIC_TYPE {
+		@Override
+		public void addFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -1004,10 +1008,13 @@ public class LINKED_CUSTOM_HASH_MAP KEY_VALUE_GENERIC_TYPE extends CUSTOM_HASH_M
 		public boolean add(KEY_TYPE o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }
 

src/builder/resources/speiger/assets/collections/templates/maps/impl/hash/LinkedOpenHashMap.template

@@ -717,6 +717,10 @@ public class LINKED_HASH_MAP KEY_VALUE_GENERIC_TYPE extends HASH_MAP KEY_VALUE_G
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<MAP.Entry KEY_VALUE_GENERIC_TYPE> implements ORDERED_MAP.FastOrderedSet KEY_VALUE_GENERIC_TYPE {
+		@Override
+		public void addFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -1003,6 +1007,12 @@ public class LINKED_HASH_MAP KEY_VALUE_GENERIC_TYPE extends HASH_MAP KEY_VALUE_G
 #endif
 		@Override
 		public boolean add(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }

src/builder/resources/speiger/assets/collections/templates/maps/impl/immutable/ImmutableOpenHashMap.template

@@ -637,6 +637,10 @@ public class IMMUTABLE_HASH_MAP KEY_VALUE_GENERIC_TYPE extends ABSTRACT_MAP KEY_
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<MAP.Entry KEY_VALUE_GENERIC_TYPE> implements ORDERED_MAP.FastOrderedSet KEY_VALUE_GENERIC_TYPE {
+		@Override
+		public void addFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -894,6 +898,12 @@ public class IMMUTABLE_HASH_MAP KEY_VALUE_GENERIC_TYPE extends ABSTRACT_MAP KEY_
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
 

src/builder/resources/speiger/assets/collections/templates/maps/impl/misc/ArrayMap.template

@@ -868,6 +868,10 @@ public class ARRAY_MAP KEY_VALUE_GENERIC_TYPE extends ABSTRACT_MAP KEY_VALUE_GEN
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<MAP.Entry KEY_VALUE_GENERIC_TYPE> implements ORDERED_MAP.FastOrderedSet KEY_VALUE_GENERIC_TYPE {
+		@Override
+		public void addFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -1126,6 +1130,10 @@ public class ARRAY_MAP KEY_VALUE_GENERIC_TYPE extends ABSTRACT_MAP KEY_VALUE_GEN
 		@Override
 		public boolean add(KEY_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }

src/builder/resources/speiger/assets/collections/templates/maps/impl/misc/LinkedEnumMap.template

@@ -473,6 +473,10 @@ public class LINKED_ENUM_MAP KEY_ENUM_VALUE_GENERIC_TYPE extends ENUM_MAP KEY_VA
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<MAP.Entry KEY_VALUE_GENERIC_TYPE> implements ORDERED_MAP.FastOrderedSet KEY_VALUE_GENERIC_TYPE {
+		@Override
+		public void addFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -637,7 +641,10 @@ public class LINKED_ENUM_MAP KEY_ENUM_VALUE_GENERIC_TYPE extends ENUM_MAP KEY_VA
 		public boolean add(T o) {
 			throw new UnsupportedOperationException();
 		}
-		
+		@Override
+		public void addFirst(T o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(T o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(T o) { throw new UnsupportedOperationException(); }
 

src/builder/resources/speiger/assets/collections/templates/sets/AbstractSet.template

@@ -73,7 +73,17 @@ public abstract class ABSTRACT_SET KEY_GENERIC_TYPE extends ABSTRACT_COLLECTION
 		public BI_ITERATOR KEY_GENERIC_TYPE reverseIterator() {
 			return set.iterator();
 		}
-
+		
+		@Override
+		public void addFirst(KEY_TYPE o) {
+			set.addLast(o);
+		}
+		
+		@Override
+		public void addLast(KEY_TYPE o) {
+			set.addFirst(o);
+		}
+		
 		@Override
 #if !TYPE_OBJECT
 		public boolean remove(KEY_TYPE o) {

src/builder/resources/speiger/assets/collections/templates/sets/ArraySet.template

@@ -153,6 +153,25 @@ public class ARRAY_SET KEY_GENERIC_TYPE extends ABSTRACT_SET KEY_GENERIC_TYPE im
 	}
 	
 #endif
+	@Override
+	public void addFirst(KEY_TYPE o) {
+		int index = findIndex(o);
+		if(index == -1) {
+			if(data.length == size) data = Arrays.copyOf(data, size == 0 ? 2 : size * 2);
+			System.arraycopy(data, 0, data, 1, size++);
+			data[0] = o;
+		}
+	}
+	
+	@Override
+	public void addLast(KEY_TYPE o) {
+		int index = findIndex(o);
+		if(index == -1) {
+			if(data.length == size) data = Arrays.copyOf(data, size == 0 ? 2 : size * 2);
+			data[size++] = o;
+		}
+	}
+	
 	@Override
 	public boolean addAndMoveToFirst(KEY_TYPE o) {
 		int index = findIndex(o);

src/builder/resources/speiger/assets/collections/templates/sets/ImmutableOpenHashSet.template

@@ -264,6 +264,10 @@ public class IMMUTABLE_HASH_SET KEY_GENERIC_TYPE extends ABSTRACT_SET KEY_GENERI
 	@Override
 	public boolean addAll(COLLECTION KEY_GENERIC_TYPE c) { throw new UnsupportedOperationException(); }
 	@Override
+	public void addFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+	@Override
+	public void addLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+	@Override
 	public boolean addAndMoveToFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
 	@Override
 	public boolean addAndMoveToLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }

src/builder/resources/speiger/assets/collections/templates/sets/LinkedOpenCustomHashSet.template

@@ -241,6 +241,46 @@ public class LINKED_CUSTOM_HASH_SET KEY_GENERIC_TYPE extends CUSTOM_HASH_SET KEY
 	}
 	
 #endif
+	@Override
+	public void addFirst(KEY_TYPE o) {
+		if(strategy.equals(o, EMPTY_KEY_VALUE)) {
+			if(containsNull) return;
+			containsNull = true;
+			onNodeAdded(nullIndex);
+			moveToFirstIndex(nullIndex);
+		}
+		else {
+			int pos = HashUtil.mix(strategy.hashCode(o)) & mask;
+			while(!strategy.equals(keys[pos], EMPTY_KEY_VALUE)) {
+				if(strategy.equals(keys[pos], o)) return;
+				pos = ++pos & mask;
+			}
+			keys[pos] = o;
+			onNodeAdded(pos);
+			moveToFirstIndex(pos);
+		}
+		if(size++ >= maxFill) rehash(HashUtil.arraySize(size+1, loadFactor));
+	}
+	
+	@Override
+	public void addLast(KEY_TYPE o) {
+		if(strategy.equals(o, EMPTY_KEY_VALUE)) {
+			if(containsNull) return;
+			containsNull = true;
+			onNodeAdded(nullIndex);
+		}
+		else {
+			int pos = HashUtil.mix(strategy.hashCode(o)) & mask;
+			while(!strategy.equals(keys[pos], EMPTY_KEY_VALUE)) {
+				if(strategy.equals(keys[pos], o)) return;
+				pos = ++pos & mask;
+			}
+			keys[pos] = o;
+			onNodeAdded(pos);
+		}
+		if(size++ >= maxFill) rehash(HashUtil.arraySize(size+1, loadFactor));
+	}
+	
 	@Override
 	public boolean addAndMoveToFirst(KEY_TYPE o) {
 		if(strategy.equals(o, EMPTY_KEY_VALUE)) {

src/builder/resources/speiger/assets/collections/templates/sets/LinkedOpenHashSet.template

@@ -212,6 +212,46 @@ public class LINKED_HASH_SET KEY_GENERIC_TYPE extends HASH_SET KEY_GENERIC_TYPE
 	}
 	
 #endif
+	@Override
+	public void addFirst(KEY_TYPE o) {
+		if(KEY_EQUALS_NULL(o)) {
+			if(containsNull) return;
+			containsNull = true;
+			onNodeAdded(nullIndex);
+			moveToFirstIndex(nullIndex);
+		}
+		else {
+			int pos = HashUtil.mix(KEY_TO_HASH(o)) & mask;
+			while(KEY_EQUALS_NOT_NULL(keys[pos])) {
+				if(KEY_EQUALS(keys[pos], o)) return;
+				pos = ++pos & mask;
+			}
+			keys[pos] = o;
+			onNodeAdded(pos);
+			moveToFirstIndex(pos);
+		}
+		if(size++ >= maxFill) rehash(HashUtil.arraySize(size+1, loadFactor));
+	}
+	
+	@Override
+	public void addLast(KEY_TYPE o) {
+		if(KEY_EQUALS_NULL(o)) {
+			if(containsNull) return;
+			containsNull = true;
+			onNodeAdded(nullIndex);
+		}
+		else {
+			int pos = HashUtil.mix(KEY_TO_HASH(o)) & mask;
+			while(KEY_EQUALS_NOT_NULL(keys[pos])) {
+				if(KEY_EQUALS(keys[pos], o)) return;
+				pos = ++pos & mask;
+			}
+			keys[pos] = o;
+			onNodeAdded(pos);
+		}
+		if(size++ >= maxFill) rehash(HashUtil.arraySize(size+1, loadFactor));
+	}
+	
 	@Override
 	public boolean addAndMoveToFirst(KEY_TYPE o) {
 		if(KEY_EQUALS_NULL(o)) {

src/builder/resources/speiger/assets/collections/templates/sets/OrderedSet.template

@@ -5,6 +5,7 @@ import java.util.SequencedSet;
 
 #endif
 import speiger.src.collections.PACKAGE.collections.BI_ITERATOR;
+import speiger.src.collections.PACKAGE.collections.ORDERED_COLLECTION;
 #if SPLIT_ITERATOR_FEATURE
 import speiger.src.collections.PACKAGE.collections.SPLIT_ITERATOR;
 import speiger.src.collections.PACKAGE.utils.SPLIT_ITERATORS;
@@ -23,9 +24,9 @@ import speiger.src.collections.PACKAGE.utils.SETS;
  * @Type(T)
  */
 #if JAVA_VERSION>=21
-public interface ORDERED_SET KEY_GENERIC_TYPE extends SET KEY_GENERIC_TYPE, SequencedSet<CLASS_TYPE>
+public interface ORDERED_SET KEY_GENERIC_TYPE extends SET KEY_GENERIC_TYPE, ORDERED_COLLECTION KEY_GENERIC_TYPE, SequencedSet<CLASS_TYPE>
 #else
-public interface ORDERED_SET KEY_GENERIC_TYPE extends SET KEY_GENERIC_TYPE
+public interface ORDERED_SET KEY_GENERIC_TYPE extends SET KEY_GENERIC_TYPE, ORDERED_COLLECTION KEY_GENERIC_TYPE
 #endif
 {
 	/**

src/builder/resources/speiger/assets/collections/templates/utils/Sets.template

@@ -360,6 +360,10 @@ public class SETS
 			s = c;
 		}
 		
+		@Override
+		public void addFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(KEY_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(KEY_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -650,7 +654,11 @@ public class SETS
 			super(c, mutex);
 			s = c;
 		}
-
+		
+		@Override
+		public void addFirst(KEY_TYPE o) { synchronized(mutex) { s.addFirst(o); } }
+		@Override
+		public void addLast(KEY_TYPE o) { synchronized(mutex) { s.addLast(o); } }
 		@Override
 		public boolean addAndMoveToFirst(KEY_TYPE o) { synchronized(mutex) { return s.addAndMoveToFirst(o); } }
 		@Override

src/builder/resources/speiger/assets/collections/templates/utils/maps/Maps.template

@@ -754,7 +754,11 @@ public class MAPS
 			super(c);
 			set = c;
 		}
-
+		
+		@Override
+		public void addFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(MAP.Entry KEY_VALUE_GENERIC_TYPE o) { throw new UnsupportedOperationException(); }
 		@Override

src/builder/resources/speiger/assets/testers/templates/builder/maps/OrderedMapTestSuiteBuilder.template

@@ -20,6 +20,7 @@ import speiger.src.testers.PACKAGE.generators.maps.TEST_ORDERED_MAP_GENERATOR;
 import speiger.src.testers.PACKAGE.impl.maps.DERIVED_MAP_GENERATORS;
 import speiger.src.testers.PACKAGE.tests.maps.FILE_KEY_TYPE2FILE_VALUE_TYPEOrderedMapMoveTester;
 import speiger.src.testers.PACKAGE.tests.maps.FILE_KEY_TYPE2FILE_VALUE_TYPEOrderedMapNavigationTester;
+import speiger.src.testers.PACKAGE.tests.maps.FILE_KEY_TYPE2FILE_VALUE_TYPEOrderedMapPutTester;
 #if !TYPE_OBJECT
 import speiger.src.testers.objects.builder.ObjectSetTestSuiteBuilder;
 import speiger.src.testers.objects.generators.TestObjectSetGenerator;
@@ -41,6 +42,7 @@ public class ORDERED_MAP_TEST_BUILDER KEY_VALUE_GENERIC_TYPE extends MAP_TEST_BU
 		List<Class<? extends AbstractTester>> testers = super.getTesters();
 		testers.add(FILE_KEY_TYPE2FILE_VALUE_TYPEOrderedMapMoveTester.class);
 		testers.add(FILE_KEY_TYPE2FILE_VALUE_TYPEOrderedMapNavigationTester.class);
+		testers.add(FILE_KEY_TYPE2FILE_VALUE_TYPEOrderedMapPutTester.class);
 		return testers;
 	}
 	

src/builder/resources/speiger/assets/testers/templates/tests/maps/MapContainsTester.template

@@ -27,6 +27,7 @@ public class FILE_KEY_TYPE2FILE_VALUE_TYPEMapContainsTester KEY_VALUE_GENERIC_TY
 
 #ignore
 	@CollectionSize.Require(absent = ZERO)
+	@SuppressWarnings("unlikely-arg-type")
 #endignore
 	public void testContainsObject_yes() {
 		assertTrue("contains(present) should return true", getMap().ENTRY_SET().contains(new AbstractMap.SimpleEntry<>(e0())));
@@ -36,6 +37,7 @@ public class FILE_KEY_TYPE2FILE_VALUE_TYPEMapContainsTester KEY_VALUE_GENERIC_TY
 		assertFalse("contains(notPresent) should return false", getMap().ENTRY_SET().contains(e3()));
 	}
 	
+	@SuppressWarnings("unlikely-arg-type")
 	public void testContainsObject_no() {
 		assertFalse("contains(notPresent) should return false", getMap().ENTRY_SET().contains(new AbstractMap.SimpleEntry<>(e3())));
 	}

src/builder/resources/speiger/assets/testers/templates/tests/maps/MapRemoveEntryTester.template

@@ -136,6 +136,7 @@ public class FILE_KEY_TYPE2FILE_VALUE_TYPEMapRemoveEntryTester KEY_VALUE_GENERIC
 #ignore
 	@CollectionSize.Require(ONE)
 	@MapFeature.Require(SUPPORTS_REMOVE)
+	@SuppressWarnings("unlikely-arg-type")
 #endignore
 	public void testRemove_supportedObjectEntryPresent() {
 		assertTrue(getMap().ENTRY_SET().remove(new AbstractMap.SimpleEntry<>(e0())));
@@ -154,6 +155,7 @@ public class FILE_KEY_TYPE2FILE_VALUE_TYPEMapRemoveEntryTester KEY_VALUE_GENERIC
 #ignore
 	@CollectionSize.Require(ONE)
 	@MapFeature.Require(SUPPORTS_REMOVE)
+	@SuppressWarnings("unlikely-arg-type")
 #endignore
 	public void testRemove_supportedObjectEntryMissing() {
 		assertFalse(getMap().ENTRY_SET().remove(new AbstractMap.SimpleEntry<>(e3())));

src/builder/resources/speiger/assets/testers/templates/tests/maps/OrderedMapPutTester.template

@@ -0,0 +1,122 @@
+package speiger.src.testers.PACKAGE.tests.maps;
+
+#ignore
+import static com.google.common.collect.testing.features.CollectionSize.ZERO;
+import static com.google.common.collect.testing.features.MapFeature.SUPPORTS_PUT;
+import static com.google.common.collect.testing.features.MapFeature.SUPPORTS_REMOVE;
+import static org.junit.Assert.assertNotEquals;
+#endignore
+
+import com.google.common.collect.testing.features.CollectionSize;
+import com.google.common.collect.testing.features.MapFeature;
+
+import speiger.src.collections.PACKAGE.maps.interfaces.MAP;
+import speiger.src.collections.PACKAGE.maps.interfaces.ORDERED_MAP;
+import speiger.src.collections.objects.lists.ObjectList;
+import speiger.src.testers.PACKAGE.tests.base.maps.ABSTRACT_MAP_TESTER;
+import speiger.src.testers.objects.utils.ObjectHelpers;
+
+@SuppressWarnings("javadoc")
+public class FILE_KEY_TYPE2FILE_VALUE_TYPEOrderedMapPutTester KEY_VALUE_GENERIC_TYPE extends ABSTRACT_MAP_TESTER KEY_VALUE_GENERIC_TYPE
+{
+	private ORDERED_MAP KEY_VALUE_GENERIC_TYPE orderedMap;
+	private ObjectList<MAP.Entry KEY_VALUE_GENERIC_TYPE> values;
+	private KEY_TYPE a;
+	private VALUE_TYPE aValue;
+	private VALUE_TYPE cValue;
+	
+	@Override
+	public void setUp() throws Exception {
+		super.setUp();
+		orderedMap = (ORDERED_MAP KEY_VALUE_GENERIC_TYPE)getMap();
+		values = ObjectHelpers.copyToList(getSampleElements(getSubjectGenerator().getCollectionSize().getNumElements()));
+		if (values.size() >= 1) {
+			a = values.get(0).ENTRY_KEY();
+			aValue = values.get(0).ENTRY_VALUE();
+			if (values.size() >= 3) {
+				cValue = values.get(2).ENTRY_VALUE();
+			}
+		}
+	}
+	
+#ignore
+	@MapFeature.Require(SUPPORTS_PUT)
+	@CollectionSize.Require(absent = ZERO)
+#endignore
+	public void testPutFirst() {
+		assertEquals(aValue, orderedMap.putFirst(a, cValue));
+		assertNotEquals(cValue, orderedMap.FIRST_ENTRY_VALUE());
+		assertEquals(orderedMap.getDefaultReturnValue(), orderedMap.putFirst(k4(), v4()));
+		assertNotEquals(v4(), orderedMap.FIRST_ENTRY_VALUE());
+		assertEquals(e4(), orderedMap.firstEntry());
+	}
+	
+
+#ignore
+	@MapFeature.Require(SUPPORTS_PUT)
+	@CollectionSize.Require(absent = ZERO)
+#endignore
+	public void testPutLast() {
+		assertEquals(aValue, orderedMap.putLast(a, cValue));
+		assertNotEquals(cValue, orderedMap.LAST_ENTRY_VALUE());
+		assertEquals(orderedMap.getDefaultReturnValue(), orderedMap.putLast(k4(), v4()));
+		assertNotEquals(v4(), orderedMap.LAST_ENTRY_VALUE());
+		assertEquals(e4(), orderedMap.lastEntry());
+	}
+	
+#ignore
+	@MapFeature.Require(SUPPORTS_REMOVE)
+	@CollectionSize.Require(CollectionSize.ONE)
+#endignore
+	public void testPollFirst() {
+		assertFalse(orderedMap.isEmpty());
+		assertEquals(e0(), orderedMap.pollFirstEntry());
+		assertTrue(orderedMap.isEmpty());
+	}
+	
+#ignore
+	@MapFeature.Require(SUPPORTS_REMOVE)
+	@CollectionSize.Require(CollectionSize.ONE)
+#endignore
+	public void testPollLast() {
+		assertFalse(orderedMap.isEmpty());
+		assertEquals(e0(), orderedMap.pollLastEntry());
+		assertTrue(orderedMap.isEmpty());
+	}
+	
+#ignore
+	@MapFeature.Require(absent = SUPPORTS_PUT)
+#endignore
+	public void testUnsupportedPutFirst() {
+		try { orderedMap.putFirst(a, aValue); }
+		catch (UnsupportedOperationException tolerated) {}
+		expectUnchanged();
+	}
+	
+#ignore
+	@MapFeature.Require(absent = SUPPORTS_PUT)
+#endignore
+	public void testUnsupportedPutLast() {
+		try { orderedMap.putLast(a, aValue); }
+		catch (UnsupportedOperationException tolerated) {}
+		expectUnchanged();
+	}
+	
+#ignore
+	@MapFeature.Require(absent = SUPPORTS_REMOVE)
+#endignore
+	public void testUnsupportedPollFirst() {
+		try { orderedMap.pollFirstEntry(); }
+		catch (UnsupportedOperationException tolerated) {}
+		expectUnchanged();
+	}
+	
+#ignore
+	@MapFeature.Require(absent = SUPPORTS_REMOVE)
+#endignore
+	public void testUnsupportedPollLast() {
+		try { orderedMap.pollFirstEntry(); }
+		catch (UnsupportedOperationException tolerated) {}
+		expectUnchanged();
+	}
+}

src/builder/resources/speiger/assets/testers/templates/tests/queue/iterators/QueueFindFirstTester.template

@@ -2,6 +2,11 @@ package speiger.src.testers.PACKAGE.tests.queue.iterators;
 
 #if TYPE_OBJECT
 import java.util.Objects;
+#endif
+#if JDK_TYPE
+import java.util.OPTIONAL;
+#else
+import speiger.src.collections.PACKAGE.functions.OPTIONAL;
 
 #endif
 import org.junit.Ignore;
@@ -27,17 +32,17 @@ public class FILE_KEY_TYPEQueueFindFirstTester KEY_GENERIC_TYPE extends ABSTRACT
 	@CollectionSize.Require(absent = CollectionSize.ZERO)
 #endignore
 	public void testQueueFindFirst_FindFirstElements() {
-		assertEquals("First Element should be found", e0(), queue.findFirst(T -> KEY_EQUALS(T, e0())));
+		assertEquals("First Element should be found", e0(), queue.findFirst(T -> KEY_EQUALS(T, e0())).SUPPLY_GET());
 	}
 	
 	public void testQueueFindFirst_FindNothing() {
-		assertEquals("No element should be found", EMPTY_KEY_VALUE, queue.findFirst(T -> KEY_EQUALS(T, e4())));
+		assertEquals("No element should be found", OPTIONAL.empty(), queue.findFirst(T -> KEY_EQUALS(T, e4())));
 	}
 	
 #ignore
 	@CollectionSize.Require(CollectionSize.SEVERAL)
 #endignore
 	public void testQueueFindFirst_FindLastElement() {
-		assertEquals("Last Element should be found", e2(), queue.findFirst(T -> KEY_EQUALS(T, e2())));
+		assertEquals("Last Element should be found", e2(), queue.findFirst(T -> KEY_EQUALS(T, e2())).SUPPLY_GET());
 	}
 }

src/builder/resources/speiger/assets/testers/templates/tests/queue/iterators/QueueReduceTester.template

@@ -3,10 +3,16 @@ package speiger.src.testers.PACKAGE.tests.queue.iterators;
 #if TYPE_OBJECT
 import java.util.Objects;
 
+#endif
+#if JDK_TYPE
+import java.util.OPTIONAL;
+#else
+import speiger.src.collections.PACKAGE.functions.OPTIONAL;
 #endif
 import org.junit.Ignore;
 
 import speiger.src.testers.PACKAGE.tests.base.ABSTRACT_QUEUE_TESTER;
+import com.google.common.collect.testing.features.CollectionSize;
 
 @Ignore
 @SuppressWarnings("javadoc")
@@ -29,7 +35,7 @@ public class FILE_KEY_TYPEQueueReduceTester KEY_GENERIC_TYPE extends ABSTRACT_QU
 	}
 	
 	public void testQueueReduce() {
-		assertEquals("The sum of the queue should match", getSum(), queue.reduce(this::sum));
+		assertEquals("The sum of the queue should match", size == CollectionSize.ZERO ? OPTIONAL.empty() : OPTIONAL.GET_OPTIONAL(getSum()), queue.reduce(this::sum));
 	}
 	
 	public void testQueueExtraReduce() {

src/main/java/speiger/src/collections/booleans/collections/BooleanIterable.java

@@ -7,6 +7,7 @@ import java.util.function.Consumer;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.booleans.functions.BooleanComparator;
 import speiger.src.collections.objects.collections.ObjectIterable;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.booleans.functions.function.BooleanFunction;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
@@ -271,13 +272,13 @@ public interface BooleanIterable extends Iterable<Boolean>
 	 * @param filter that should be applied
 	 * @return the found value or the null equivalent variant.
 	 */
-	default boolean findFirst(BooleanPredicate filter) {
+	default OptionalBoolean findFirst(BooleanPredicate filter) {
 		Objects.requireNonNull(filter);
 		for(BooleanIterator iter = iterator();iter.hasNext();) {
 			boolean entry = iter.nextBoolean();
-			if(filter.test(entry)) return entry;
+			if(filter.test(entry)) return OptionalBoolean.of(entry);
 		}
-		return false;
+		return OptionalBoolean.empty();
 	}
 	
 	/**
@@ -302,7 +303,7 @@ public interface BooleanIterable extends Iterable<Boolean>
 	 * @param operator the operation that should be applied
 	 * @return the reduction result, returns null value if nothing was found
 	 */
-	default boolean reduce(BooleanBooleanUnaryOperator operator) {
+	default OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		boolean state = false;
 		boolean empty = true;
@@ -314,7 +315,7 @@ public interface BooleanIterable extends Iterable<Boolean>
 			}
 			state = operator.applyAsBoolean(state, iter.nextBoolean());
 		}
-		return state;
+		return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 	}	
 	
 	/**

src/main/java/speiger/src/collections/booleans/lists/BooleanArrayList.java

@@ -10,6 +10,7 @@ import java.util.function.UnaryOperator;
 import speiger.src.collections.booleans.collections.BooleanCollection;
 import speiger.src.collections.booleans.collections.BooleanStack;
 import speiger.src.collections.booleans.collections.BooleanIterator;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.booleans.functions.BooleanComparator;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
@@ -510,12 +511,12 @@ public class BooleanArrayList extends AbstractBooleanList implements IBooleanArr
 	}
 	
 	@Override
-	public boolean findFirst(BooleanPredicate filter) {
+	public OptionalBoolean findFirst(BooleanPredicate filter) {
 		Objects.requireNonNull(filter);
 		for(int i = 0;i<size;i++) {
-			if(filter.test(data[i])) return data[i];
+			if(filter.test(data[i])) return OptionalBoolean.of(data[i]);
 		}
-		return false;
+		return OptionalBoolean.empty();
 	}
 	
 	@Override
@@ -529,7 +530,7 @@ public class BooleanArrayList extends AbstractBooleanList implements IBooleanArr
 	}
 	
 	@Override
-	public boolean reduce(BooleanBooleanUnaryOperator operator) {
+	public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		boolean state = false;
 		boolean empty = true;
@@ -541,7 +542,7 @@ public class BooleanArrayList extends AbstractBooleanList implements IBooleanArr
 			}
 			state = operator.applyAsBoolean(state, data[i]);
 		}
-		return state;
+		return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/booleans/lists/BooleanLinkedList.java

@@ -8,6 +8,7 @@ import java.util.Spliterator;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
 import java.util.function.UnaryOperator;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
@@ -415,12 +416,12 @@ public class BooleanLinkedList extends AbstractBooleanList implements BooleanPri
 	}
 	
 	@Override
-	public boolean findFirst(BooleanPredicate filter) {
+	public OptionalBoolean findFirst(BooleanPredicate filter) {
 		Objects.requireNonNull(filter);
 		for(Entry entry = first;entry != null;entry = entry.next) {
-			if(filter.test(entry.value)) return entry.value;
+			if(filter.test(entry.value)) return OptionalBoolean.of(entry.value);
 		}
-		return false;
+		return OptionalBoolean.empty();
 	}
 	
 	@Override
@@ -434,7 +435,7 @@ public class BooleanLinkedList extends AbstractBooleanList implements BooleanPri
 	}
 	
 	@Override
-	public boolean reduce(BooleanBooleanUnaryOperator operator) {
+	public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		boolean state = false;
 		boolean empty = true;
@@ -446,7 +447,7 @@ public class BooleanLinkedList extends AbstractBooleanList implements BooleanPri
 			}
 			state = operator.applyAsBoolean(state, entry.value);
 		}
-		return state;
+		return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/booleans/lists/CopyOnWriteBooleanArrayList.java

@@ -14,6 +14,7 @@ import java.util.function.UnaryOperator;
 import speiger.src.collections.booleans.collections.BooleanCollection;
 import speiger.src.collections.booleans.collections.BooleanStack;
 import speiger.src.collections.booleans.collections.BooleanIterator;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.booleans.functions.BooleanComparator;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
@@ -645,13 +646,13 @@ public class CopyOnWriteBooleanArrayList extends AbstractBooleanList implements
 	}
 	
 	@Override
-	public boolean findFirst(BooleanPredicate filter) {
+	public OptionalBoolean findFirst(BooleanPredicate filter) {
 		Objects.requireNonNull(filter);
 		boolean[] data = this.data;
 		for(int i = 0,m=data.length;i<m;i++) {
-			if(filter.test(data[i])) return data[i];
+			if(filter.test(data[i])) return OptionalBoolean.of(data[i]);
 		}
-		return false;
+		return OptionalBoolean.empty();
 	}
 	
 	@Override
@@ -666,7 +667,7 @@ public class CopyOnWriteBooleanArrayList extends AbstractBooleanList implements
 	}
 	
 	@Override
-	public boolean reduce(BooleanBooleanUnaryOperator operator) {
+	public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		boolean[] data = this.data;
 		boolean state = false;
@@ -679,7 +680,7 @@ public class CopyOnWriteBooleanArrayList extends AbstractBooleanList implements
 			}
 			state = operator.applyAsBoolean(state, data[i]);
 		}
-		return state;
+		return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/booleans/lists/ImmutableBooleanList.java

@@ -10,6 +10,7 @@ import java.util.function.UnaryOperator;
 import speiger.src.collections.booleans.collections.BooleanCollection;
 import speiger.src.collections.booleans.functions.BooleanComparator;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.booleans.utils.BooleanArrays;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
@@ -270,12 +271,12 @@ public class ImmutableBooleanList extends AbstractBooleanList
 	}
 	
 	@Override
-	public boolean findFirst(BooleanPredicate filter) {
+	public OptionalBoolean findFirst(BooleanPredicate filter) {
 		Objects.requireNonNull(filter);
 		for(int i = 0,m=data.length;i<m;i++) {
-			if(filter.test(data[i])) return data[i];
+			if(filter.test(data[i])) return OptionalBoolean.of(data[i]);
 		}
-		return false;
+		return OptionalBoolean.empty();
 	}
 	
 	@Override
@@ -289,7 +290,7 @@ public class ImmutableBooleanList extends AbstractBooleanList
 	}
 	
 	@Override
-	public boolean reduce(BooleanBooleanUnaryOperator operator) {
+	public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		boolean state = false;
 		boolean empty = true;
@@ -301,7 +302,7 @@ public class ImmutableBooleanList extends AbstractBooleanList
 			}
 			state = operator.applyAsBoolean(state, data[i]);
 		}
-		return state;
+		return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/booleans/queues/BooleanArrayFIFOQueue.java

@@ -5,6 +5,7 @@ import java.util.Objects;
 import java.util.NoSuchElementException;
 
 import speiger.src.collections.booleans.collections.BooleanIterator;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.booleans.functions.BooleanComparator;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
@@ -278,17 +279,17 @@ public class BooleanArrayFIFOQueue extends AbstractBooleanPriorityQueue implemen
 	}
 	
 	@Override
-	public boolean findFirst(BooleanPredicate filter) {
+	public OptionalBoolean findFirst(BooleanPredicate filter) {
 		Objects.requireNonNull(filter);
 		for(int i = 0,m=size();i<m;i++) {
 			int index = (first + i) % array.length;
 			if(filter.test(array[index])) {
 				boolean data = array[index];
 				removeIndex(index);
-				return data;
+				return OptionalBoolean.of(data);
 			}
 		}
-		return false;
+		return OptionalBoolean.empty();
 	}
 	
 	@Override
@@ -302,7 +303,7 @@ public class BooleanArrayFIFOQueue extends AbstractBooleanPriorityQueue implemen
 	}
 	
 	@Override
-	public boolean reduce(BooleanBooleanUnaryOperator operator) {
+	public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		boolean state = false;
 		boolean empty = true;
@@ -314,7 +315,7 @@ public class BooleanArrayFIFOQueue extends AbstractBooleanPriorityQueue implemen
 			}
 			state = operator.applyAsBoolean(state, array[(first + i) % array.length]);
 		}
-		return state;
+		return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/booleans/queues/BooleanArrayPriorityQueue.java

@@ -6,6 +6,7 @@ import java.util.Objects;
 
 import speiger.src.collections.booleans.collections.BooleanCollection;
 import speiger.src.collections.booleans.collections.BooleanIterator;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.booleans.functions.BooleanComparator;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
@@ -307,7 +308,7 @@ public class BooleanArrayPriorityQueue extends AbstractBooleanPriorityQueue
 	}
 	
 	@Override
-	public boolean reduce(BooleanBooleanUnaryOperator operator) {
+	public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		boolean state = false;
 		boolean empty = true;
@@ -319,20 +320,20 @@ public class BooleanArrayPriorityQueue extends AbstractBooleanPriorityQueue
 			}
 			state = operator.applyAsBoolean(state, array[i]);
 		}
-		return state;
+		return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 	}
 	
 	@Override
-	public boolean findFirst(BooleanPredicate filter) {
+	public OptionalBoolean findFirst(BooleanPredicate filter) {
 		Objects.requireNonNull(filter);
 		for(int i = 0;i<size;i++) {
 			if(filter.test(array[i])) {
 				boolean data = array[i];
 				removeIndex(i);
-				return data;
+				return OptionalBoolean.of(data);
 			}
 		}
-		return false;
+		return OptionalBoolean.empty();
 	}
 	
 	@Override

src/main/java/speiger/src/collections/booleans/queues/BooleanHeapPriorityQueue.java

@@ -6,6 +6,7 @@ import java.util.Objects;
 
 import speiger.src.collections.booleans.collections.BooleanCollection;
 import speiger.src.collections.booleans.collections.BooleanIterator;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.booleans.functions.BooleanComparator;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
@@ -290,7 +291,7 @@ public class BooleanHeapPriorityQueue extends AbstractBooleanPriorityQueue
 	}
 	
 	@Override
-	public boolean reduce(BooleanBooleanUnaryOperator operator) {
+	public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		boolean state = false;
 		boolean empty = true;
@@ -302,20 +303,20 @@ public class BooleanHeapPriorityQueue extends AbstractBooleanPriorityQueue
 			}
 			state = operator.applyAsBoolean(state, array[i]);
 		}
-		return state;
+		return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 	}
 	
 	@Override
-	public boolean findFirst(BooleanPredicate filter) {
+	public OptionalBoolean findFirst(BooleanPredicate filter) {
 		Objects.requireNonNull(filter);
 		for(int i = 0;i<size;i++) {
 			if(filter.test(array[i])) {
 				boolean data = array[i];
 				removeIndex(i);
-				return data;
+				return OptionalBoolean.of(data);
 			}
 		}
-		return false;
+		return OptionalBoolean.empty();
 	}
 	
 	@Override

src/main/java/speiger/src/collections/booleans/utils/BooleanCollections.java

@@ -13,6 +13,7 @@ import speiger.src.collections.booleans.collections.BooleanCollection;
 import speiger.src.collections.booleans.collections.BooleanOrderedCollection;
 import speiger.src.collections.booleans.collections.BooleanIterator;
 import speiger.src.collections.booleans.functions.BooleanComparator;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.utils.ObjectArrays;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
@@ -460,9 +461,9 @@ public class BooleanCollections
 		@Override
 		public boolean reduce(boolean identity, BooleanBooleanUnaryOperator operator) { synchronized(mutex) { return c.reduce(identity, operator); } }
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) { synchronized(mutex) { return c.reduce(operator); } }
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) { synchronized(mutex) { return c.reduce(operator); } }
 		@Override
-		public boolean findFirst(BooleanPredicate filter) { synchronized(mutex) { return c.findFirst(filter); } }
+		public OptionalBoolean findFirst(BooleanPredicate filter) { synchronized(mutex) { return c.findFirst(filter); } }
 		@Override
 		public int count(BooleanPredicate filter) { synchronized(mutex) { return c.count(filter); } }
 	}
@@ -588,9 +589,9 @@ public class BooleanCollections
 		@Override
 		public boolean reduce(boolean identity, BooleanBooleanUnaryOperator operator) { return c.reduce(identity, operator); }
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) { return c.reduce(operator); }
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) { return c.reduce(operator); }
 		@Override
-		public boolean findFirst(BooleanPredicate filter) { return c.findFirst(filter); }
+		public OptionalBoolean findFirst(BooleanPredicate filter) { return c.findFirst(filter); }
 		@Override
 		public int count(BooleanPredicate filter) { return c.count(filter); }
 	}

src/main/java/speiger/src/collections/booleans/utils/BooleanPriorityQueues.java

@@ -1,13 +1,14 @@
 package speiger.src.collections.booleans.utils;
 
-
 import speiger.src.collections.booleans.collections.BooleanIterator;
 import speiger.src.collections.booleans.collections.BooleanCollection;
 import speiger.src.collections.booleans.functions.BooleanComparator;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.booleans.queues.BooleanPriorityDequeue;
 import speiger.src.collections.booleans.queues.BooleanPriorityQueue;
 import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.function.BooleanBooleanUnaryOperator;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 
 /**
@@ -113,7 +114,11 @@ public class BooleanPriorityQueues
 		@Override
 		public boolean matchesAll(BooleanPredicate filter) { synchronized(mutex) { return queue.matchesAll(filter); } }
 		@Override
-		public boolean findFirst(BooleanPredicate filter) { synchronized(mutex) { return queue.findFirst(filter); } }
+		public OptionalBoolean findFirst(BooleanPredicate filter) { synchronized(mutex) { return queue.findFirst(filter); } }
+		@Override
+		public boolean reduce(boolean identity, BooleanBooleanUnaryOperator operator) { synchronized(mutex) { return queue.reduce(identity, operator); } }
+		@Override
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) { synchronized(mutex) { return queue.reduce(operator); } }
 		@Override
 		public int count(BooleanPredicate filter) { synchronized(mutex) { return queue.count(filter); } }
 	}

src/main/java/speiger/src/collections/bytes/collections/ByteIterable.java

@@ -7,6 +7,7 @@ import java.util.function.Consumer;
 import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.bytes.functions.ByteComparator;
 import speiger.src.collections.objects.collections.ObjectIterable;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.ByteFunction;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
@@ -281,13 +282,13 @@ public interface ByteIterable extends Iterable<Byte>
 	 * @param filter that should be applied
 	 * @return the found value or the null equivalent variant.
 	 */
-	default byte findFirst(BytePredicate filter) {
+	default OptionalByte findFirst(BytePredicate filter) {
 		Objects.requireNonNull(filter);
 		for(ByteIterator iter = iterator();iter.hasNext();) {
 			byte entry = iter.nextByte();
-			if(filter.test(entry)) return entry;
+			if(filter.test(entry)) return OptionalByte.of(entry);
 		}
-		return (byte)0;
+		return OptionalByte.empty();
 	}
 	
 	/**
@@ -312,7 +313,7 @@ public interface ByteIterable extends Iterable<Byte>
 	 * @param operator the operation that should be applied
 	 * @return the reduction result, returns null value if nothing was found
 	 */
-	default byte reduce(ByteByteUnaryOperator operator) {
+	default OptionalByte reduce(ByteByteUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		byte state = (byte)0;
 		boolean empty = true;
@@ -324,7 +325,7 @@ public interface ByteIterable extends Iterable<Byte>
 			}
 			state = operator.applyAsByte(state, iter.nextByte());
 		}
-		return state;
+		return empty ? OptionalByte.empty() : OptionalByte.of(state);
 	}	
 	
 	/**

src/main/java/speiger/src/collections/bytes/lists/ByteArrayList.java

@@ -12,6 +12,7 @@ import java.nio.ByteBuffer;
 import speiger.src.collections.bytes.collections.ByteCollection;
 import speiger.src.collections.bytes.collections.ByteStack;
 import speiger.src.collections.bytes.collections.ByteIterator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.ByteComparator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
@@ -519,12 +520,12 @@ public class ByteArrayList extends AbstractByteList implements IByteArray, ByteS
 	}
 	
 	@Override
-	public byte findFirst(BytePredicate filter) {
+	public OptionalByte findFirst(BytePredicate filter) {
 		Objects.requireNonNull(filter);
 		for(int i = 0;i<size;i++) {
-			if(filter.test(data[i])) return data[i];
+			if(filter.test(data[i])) return OptionalByte.of(data[i]);
 		}
-		return (byte)0;
+		return OptionalByte.empty();
 	}
 	
 	@Override
@@ -538,7 +539,7 @@ public class ByteArrayList extends AbstractByteList implements IByteArray, ByteS
 	}
 	
 	@Override
-	public byte reduce(ByteByteUnaryOperator operator) {
+	public OptionalByte reduce(ByteByteUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		byte state = (byte)0;
 		boolean empty = true;
@@ -550,7 +551,7 @@ public class ByteArrayList extends AbstractByteList implements IByteArray, ByteS
 			}
 			state = operator.applyAsByte(state, data[i]);
 		}
-		return state;
+		return empty ? OptionalByte.empty() : OptionalByte.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/bytes/lists/ByteLinkedList.java

@@ -11,6 +11,7 @@ import java.util.function.Consumer;
 import java.util.function.Predicate;
 import java.util.function.UnaryOperator;
 import java.util.function.IntPredicate;import java.util.function.IntUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
@@ -429,12 +430,12 @@ public class ByteLinkedList extends AbstractByteList implements BytePriorityDequ
 	}
 	
 	@Override
-	public byte findFirst(BytePredicate filter) {
+	public OptionalByte findFirst(BytePredicate filter) {
 		Objects.requireNonNull(filter);
 		for(Entry entry = first;entry != null;entry = entry.next) {
-			if(filter.test(entry.value)) return entry.value;
+			if(filter.test(entry.value)) return OptionalByte.of(entry.value);
 		}
-		return (byte)0;
+		return OptionalByte.empty();
 	}
 	
 	@Override
@@ -448,7 +449,7 @@ public class ByteLinkedList extends AbstractByteList implements BytePriorityDequ
 	}
 	
 	@Override
-	public byte reduce(ByteByteUnaryOperator operator) {
+	public OptionalByte reduce(ByteByteUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		byte state = (byte)0;
 		boolean empty = true;
@@ -460,7 +461,7 @@ public class ByteLinkedList extends AbstractByteList implements BytePriorityDequ
 			}
 			state = operator.applyAsByte(state, entry.value);
 		}
-		return state;
+		return empty ? OptionalByte.empty() : OptionalByte.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/bytes/lists/CopyOnWriteByteArrayList.java

@@ -16,6 +16,7 @@ import java.nio.ByteBuffer;
 import speiger.src.collections.bytes.collections.ByteCollection;
 import speiger.src.collections.bytes.collections.ByteStack;
 import speiger.src.collections.bytes.collections.ByteIterator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.ByteComparator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
@@ -654,13 +655,13 @@ public class CopyOnWriteByteArrayList extends AbstractByteList implements ITrimm
 	}
 	
 	@Override
-	public byte findFirst(BytePredicate filter) {
+	public OptionalByte findFirst(BytePredicate filter) {
 		Objects.requireNonNull(filter);
 		byte[] data = this.data;
 		for(int i = 0,m=data.length;i<m;i++) {
-			if(filter.test(data[i])) return data[i];
+			if(filter.test(data[i])) return OptionalByte.of(data[i]);
 		}
-		return (byte)0;
+		return OptionalByte.empty();
 	}
 	
 	@Override
@@ -675,7 +676,7 @@ public class CopyOnWriteByteArrayList extends AbstractByteList implements ITrimm
 	}
 	
 	@Override
-	public byte reduce(ByteByteUnaryOperator operator) {
+	public OptionalByte reduce(ByteByteUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		byte[] data = this.data;
 		byte state = (byte)0;
@@ -688,7 +689,7 @@ public class CopyOnWriteByteArrayList extends AbstractByteList implements ITrimm
 			}
 			state = operator.applyAsByte(state, data[i]);
 		}
-		return state;
+		return empty ? OptionalByte.empty() : OptionalByte.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/bytes/lists/ImmutableByteList.java

@@ -11,6 +11,7 @@ import java.util.function.IntPredicate;import java.util.function.IntUnaryOperato
 import speiger.src.collections.bytes.collections.ByteCollection;
 import speiger.src.collections.bytes.functions.ByteComparator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.utils.ByteArrays;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
@@ -273,12 +274,12 @@ public class ImmutableByteList extends AbstractByteList
 	}
 	
 	@Override
-	public byte findFirst(BytePredicate filter) {
+	public OptionalByte findFirst(BytePredicate filter) {
 		Objects.requireNonNull(filter);
 		for(int i = 0,m=data.length;i<m;i++) {
-			if(filter.test(data[i])) return data[i];
+			if(filter.test(data[i])) return OptionalByte.of(data[i]);
 		}
-		return (byte)0;
+		return OptionalByte.empty();
 	}
 	
 	@Override
@@ -292,7 +293,7 @@ public class ImmutableByteList extends AbstractByteList
 	}
 	
 	@Override
-	public byte reduce(ByteByteUnaryOperator operator) {
+	public OptionalByte reduce(ByteByteUnaryOperator operator) {
 		Objects.requireNonNull(operator);
 		byte state = (byte)0;
 		boolean empty = true;
@@ -304,7 +305,7 @@ public class ImmutableByteList extends AbstractByteList
 			}
 			state = operator.applyAsByte(state, data[i]);
 		}
-		return state;
+		return empty ? OptionalByte.empty() : OptionalByte.of(state);
 	}
 	
 	@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2BooleanConcurrentOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.function.ByteBooleanUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2BooleanMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2BooleanMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2BooleanConcurrentMap;
@@ -36,6 +38,7 @@ import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -755,7 +758,7 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -779,11 +782,11 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -793,7 +796,7 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -801,7 +804,7 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1062,7 +1065,7 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1086,11 +1089,11 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
@@ -1098,7 +1101,7 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1106,7 +1109,7 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1297,7 +1300,7 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -1321,20 +1324,20 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return false;
+			if(size() <= 0) return OptionalBoolean.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return OptionalBoolean.of(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1342,7 +1345,7 @@ public class Byte2BooleanConcurrentOpenHashMap extends AbstractByte2BooleanMap i
 					seg.unlockRead(stamp);
 				}
 			}
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2ByteConcurrentOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
@@ -18,6 +19,7 @@ import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.bytes.functions.consumer.ByteByteConsumer;
 import speiger.src.collections.bytes.functions.function.ByteUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ByteMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ByteMap;
@@ -761,7 +763,7 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
+		public Optional<Byte2ByteMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ByteMap.Entry state = null;
 			boolean empty = true;
@@ -785,11 +787,11 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry findFirst(Predicate<Byte2ByteMap.Entry> filter) {
+		public Optional<Byte2ByteMap.Entry> findFirst(Predicate<Byte2ByteMap.Entry> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -799,7 +801,7 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -807,7 +809,7 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1068,7 +1070,7 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1092,11 +1094,11 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
@@ -1104,7 +1106,7 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1112,7 +1114,7 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1303,7 +1305,7 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1327,20 +1329,20 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return OptionalByte.of(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1348,7 +1350,7 @@ public class Byte2ByteConcurrentOpenHashMap extends AbstractByte2ByteMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2CharConcurrentOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteCharConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2CharFunction;
 import speiger.src.collections.bytes.functions.function.ByteCharUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2CharMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2CharMap;
@@ -37,6 +39,7 @@ import speiger.src.collections.chars.functions.CharConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectCharConsumer;
 import speiger.src.collections.chars.functions.function.CharPredicate;
+import speiger.src.collections.chars.functions.OptionalChar;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -768,7 +771,7 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 		}
 		
 		@Override
-		public Byte2CharMap.Entry reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
+		public Optional<Byte2CharMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2CharMap.Entry state = null;
 			boolean empty = true;
@@ -792,11 +795,11 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2CharMap.Entry findFirst(Predicate<Byte2CharMap.Entry> filter) {
+		public Optional<Byte2CharMap.Entry> findFirst(Predicate<Byte2CharMap.Entry> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -806,7 +809,7 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -814,7 +817,7 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1075,7 +1078,7 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1099,11 +1102,11 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
@@ -1111,7 +1114,7 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1119,7 +1122,7 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1310,7 +1313,7 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 		}
 		
 		@Override
-		public char reduce(CharCharUnaryOperator operator) {
+		public OptionalChar reduce(CharCharUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			char state = (char)0;
 			boolean empty = true;
@@ -1334,20 +1337,20 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalChar.empty() : OptionalChar.of(state);
 		}
 		
 		@Override
-		public char findFirst(CharPredicate filter) {
+		public OptionalChar findFirst(CharPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (char)0;
+			if(size() <= 0) return OptionalChar.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return OptionalChar.of(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1355,7 +1358,7 @@ public class Byte2CharConcurrentOpenHashMap extends AbstractByte2CharMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return (char)0;
+			return OptionalChar.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2DoubleConcurrentOpenHashMap.java

@@ -4,11 +4,13 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
 import java.util.function.BiFunction;
 import java.util.function.DoublePredicate;
+import java.util.OptionalDouble;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteDoubleConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2DoubleFunction;
 import speiger.src.collections.bytes.functions.function.ByteDoubleUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2DoubleMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2DoubleMap;
@@ -768,7 +771,7 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
+		public Optional<Byte2DoubleMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2DoubleMap.Entry state = null;
 			boolean empty = true;
@@ -792,11 +795,11 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
+		public Optional<Byte2DoubleMap.Entry> findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -806,7 +809,7 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -814,7 +817,7 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1075,7 +1078,7 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1099,11 +1102,11 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
@@ -1111,7 +1114,7 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1119,7 +1122,7 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1310,7 +1313,7 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 		}
 		
 		@Override
-		public double reduce(DoubleDoubleUnaryOperator operator) {
+		public OptionalDouble reduce(DoubleDoubleUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			double state = 0D;
 			boolean empty = true;
@@ -1334,20 +1337,20 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalDouble.empty() : OptionalDouble.of(state);
 		}
 		
 		@Override
-		public double findFirst(DoublePredicate filter) {
+		public OptionalDouble findFirst(DoublePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0D;
+			if(size() <= 0) return OptionalDouble.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return OptionalDouble.of(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1355,7 +1358,7 @@ public class Byte2DoubleConcurrentOpenHashMap extends AbstractByte2DoubleMap imp
 					seg.unlockRead(stamp);
 				}
 			}
-			return 0D;
+			return OptionalDouble.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2FloatConcurrentOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteFloatConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2FloatFunction;
 import speiger.src.collections.bytes.functions.function.ByteFloatUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2FloatMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2FloatMap;
@@ -37,6 +39,7 @@ import speiger.src.collections.floats.functions.FloatConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectFloatConsumer;
 import speiger.src.collections.floats.functions.function.FloatPredicate;
+import speiger.src.collections.floats.functions.OptionalFloat;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -768,7 +771,7 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
+		public Optional<Byte2FloatMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2FloatMap.Entry state = null;
 			boolean empty = true;
@@ -792,11 +795,11 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry findFirst(Predicate<Byte2FloatMap.Entry> filter) {
+		public Optional<Byte2FloatMap.Entry> findFirst(Predicate<Byte2FloatMap.Entry> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -806,7 +809,7 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -814,7 +817,7 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1075,7 +1078,7 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1099,11 +1102,11 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
@@ -1111,7 +1114,7 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1119,7 +1122,7 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1310,7 +1313,7 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 		}
 		
 		@Override
-		public float reduce(FloatFloatUnaryOperator operator) {
+		public OptionalFloat reduce(FloatFloatUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			float state = 0F;
 			boolean empty = true;
@@ -1334,20 +1337,20 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalFloat.empty() : OptionalFloat.of(state);
 		}
 		
 		@Override
-		public float findFirst(FloatPredicate filter) {
+		public OptionalFloat findFirst(FloatPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0F;
+			if(size() <= 0) return OptionalFloat.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return OptionalFloat.of(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1355,7 +1358,7 @@ public class Byte2FloatConcurrentOpenHashMap extends AbstractByte2FloatMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return 0F;
+			return OptionalFloat.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2IntConcurrentOpenHashMap.java

@@ -4,11 +4,13 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
 import java.util.function.BiFunction;
 import java.util.function.IntPredicate;
+import java.util.OptionalInt;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteIntConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2IntFunction;
 import speiger.src.collections.bytes.functions.function.ByteIntUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2IntMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2IntMap;
@@ -768,7 +771,7 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 		}
 		
 		@Override
-		public Byte2IntMap.Entry reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
+		public Optional<Byte2IntMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2IntMap.Entry state = null;
 			boolean empty = true;
@@ -792,11 +795,11 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2IntMap.Entry findFirst(Predicate<Byte2IntMap.Entry> filter) {
+		public Optional<Byte2IntMap.Entry> findFirst(Predicate<Byte2IntMap.Entry> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -806,7 +809,7 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -814,7 +817,7 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1075,7 +1078,7 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1099,11 +1102,11 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
@@ -1111,7 +1114,7 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1119,7 +1122,7 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1310,7 +1313,7 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 		}
 		
 		@Override
-		public int reduce(IntIntUnaryOperator operator) {
+		public OptionalInt reduce(IntIntUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			int state = 0;
 			boolean empty = true;
@@ -1334,20 +1337,20 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalInt.empty() : OptionalInt.of(state);
 		}
 		
 		@Override
-		public int findFirst(IntPredicate filter) {
+		public OptionalInt findFirst(IntPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0;
+			if(size() <= 0) return OptionalInt.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return OptionalInt.of(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1355,7 +1358,7 @@ public class Byte2IntConcurrentOpenHashMap extends AbstractByte2IntMap implement
 					seg.unlockRead(stamp);
 				}
 			}
-			return 0;
+			return OptionalInt.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2LongConcurrentOpenHashMap.java

@@ -4,11 +4,13 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
 import java.util.function.BiFunction;
 import java.util.function.LongPredicate;
+import java.util.OptionalLong;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteLongConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2LongFunction;
 import speiger.src.collections.bytes.functions.function.ByteLongUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2LongMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2LongMap;
@@ -768,7 +771,7 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 		}
 		
 		@Override
-		public Byte2LongMap.Entry reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
+		public Optional<Byte2LongMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2LongMap.Entry state = null;
 			boolean empty = true;
@@ -792,11 +795,11 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2LongMap.Entry findFirst(Predicate<Byte2LongMap.Entry> filter) {
+		public Optional<Byte2LongMap.Entry> findFirst(Predicate<Byte2LongMap.Entry> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -806,7 +809,7 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -814,7 +817,7 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1075,7 +1078,7 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1099,11 +1102,11 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
@@ -1111,7 +1114,7 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1119,7 +1122,7 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1310,7 +1313,7 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 		}
 		
 		@Override
-		public long reduce(LongLongUnaryOperator operator) {
+		public OptionalLong reduce(LongLongUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			long state = 0L;
 			boolean empty = true;
@@ -1334,20 +1337,20 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalLong.empty() : OptionalLong.of(state);
 		}
 		
 		@Override
-		public long findFirst(LongPredicate filter) {
+		public OptionalLong findFirst(LongPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0L;
+			if(size() <= 0) return OptionalLong.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return OptionalLong.of(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1355,7 +1358,7 @@ public class Byte2LongConcurrentOpenHashMap extends AbstractByte2LongMap impleme
 					seg.unlockRead(stamp);
 				}
 			}
-			return 0L;
+			return OptionalLong.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2ObjectConcurrentOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
@@ -18,6 +19,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteObjectConsumer;
 import speiger.src.collections.bytes.functions.function.ByteFunction;
 import speiger.src.collections.bytes.functions.function.ByteObjectUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ObjectMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ObjectMap;
@@ -715,7 +717,7 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
+		public Optional<Byte2ObjectMap.Entry<V>> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ObjectMap.Entry<V> state = null;
 			boolean empty = true;
@@ -739,11 +741,11 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
+		public Optional<Byte2ObjectMap.Entry<V>> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -753,7 +755,7 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -761,7 +763,7 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1022,7 +1024,7 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1046,11 +1048,11 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment<V> seg = segments[i];
@@ -1058,7 +1060,7 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1066,7 +1068,7 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1258,7 +1260,7 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 		}
 		
 		@Override
-		public V reduce(ObjectObjectUnaryOperator<V, V> operator) {
+		public Optional<V> reduce(ObjectObjectUnaryOperator<V, V> operator) {
 			Objects.requireNonNull(operator);
 			V state = null;
 			boolean empty = true;
@@ -1282,20 +1284,20 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public V findFirst(Predicate<V> filter) {
+		public Optional<V> findFirst(Predicate<V> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment<V> seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return Optional.ofNullable(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1303,7 +1305,7 @@ public class Byte2ObjectConcurrentOpenHashMap<V> extends AbstractByte2ObjectMap<
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/concurrent/Byte2ShortConcurrentOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.concurrent.locks.StampedLock;
 import java.util.function.Consumer;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteShortConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2ShortFunction;
 import speiger.src.collections.bytes.functions.function.ByteShortUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ShortMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ShortMap;
@@ -37,6 +39,7 @@ import speiger.src.collections.shorts.functions.ShortConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectShortConsumer;
 import speiger.src.collections.shorts.functions.function.ShortPredicate;
+import speiger.src.collections.shorts.functions.OptionalShort;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -768,7 +771,7 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
+		public Optional<Byte2ShortMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ShortMap.Entry state = null;
 			boolean empty = true;
@@ -792,11 +795,11 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry findFirst(Predicate<Byte2ShortMap.Entry> filter) {
+		public Optional<Byte2ShortMap.Entry> findFirst(Predicate<Byte2ShortMap.Entry> filter) {
 			Objects.requireNonNull(filter);
 			MapEntry entry = new MapEntry();
 			for(int i = 0,m=segments.length;i<m;i++) {
@@ -806,7 +809,7 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 				try {
 					while(index != -1) {
 						entry.set(index, i);
-						if(filter.test(entry)) return entry;
+						if(filter.test(entry)) return Optional.ofNullable(entry);
 						index = (int)seg.links[index];
 					}
 				}
@@ -814,7 +817,7 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1075,7 +1078,7 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1099,11 +1102,11 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
@@ -1111,7 +1114,7 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.keys[index])) return seg.keys[index];
+						if(filter.test(seg.keys[index])) return OptionalByte.of(seg.keys[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1119,7 +1122,7 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1310,7 +1313,7 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 		}
 		
 		@Override
-		public short reduce(ShortShortUnaryOperator operator) {
+		public OptionalShort reduce(ShortShortUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			short state = (short)0;
 			boolean empty = true;
@@ -1334,20 +1337,20 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return state;
+			return empty ? OptionalShort.empty() : OptionalShort.of(state);
 		}
 		
 		@Override
-		public short findFirst(ShortPredicate filter) {
+		public OptionalShort findFirst(ShortPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (short)0;
+			if(size() <= 0) return OptionalShort.empty();
 			for(int i = 0,m=segments.length;i<m;i++) {
 				Segment seg = segments[i];
 				long stamp = seg.readLock();
 				try {
 					int index = seg.firstIndex;
 					while(index != -1){
-						if(filter.test(seg.values[index])) return seg.values[index];
+						if(filter.test(seg.values[index])) return OptionalShort.of(seg.values[index]);
 						index = (int)seg.links[index];
 					}
 				}
@@ -1355,7 +1358,7 @@ public class Byte2ShortConcurrentOpenHashMap extends AbstractByte2ShortMap imple
 					seg.unlockRead(stamp);
 				}
 			}
-			return (short)0;
+			return OptionalShort.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2BooleanLinkedOpenCustomHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -33,6 +35,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.lists.ObjectListIterator;
@@ -671,6 +674,10 @@ public class Byte2BooleanLinkedOpenCustomHashMap extends Byte2BooleanOpenCustomH
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2BooleanMap.Entry> implements Byte2BooleanOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -836,7 +843,7 @@ public class Byte2BooleanLinkedOpenCustomHashMap extends Byte2BooleanOpenCustomH
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -851,21 +858,21 @@ public class Byte2BooleanLinkedOpenCustomHashMap extends Byte2BooleanOpenCustomH
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -944,10 +951,13 @@ public class Byte2BooleanLinkedOpenCustomHashMap extends Byte2BooleanOpenCustomH
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1090,7 +1100,7 @@ public class Byte2BooleanLinkedOpenCustomHashMap extends Byte2BooleanOpenCustomH
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1105,19 +1115,19 @@ public class Byte2BooleanLinkedOpenCustomHashMap extends Byte2BooleanOpenCustomH
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1252,7 +1262,7 @@ public class Byte2BooleanLinkedOpenCustomHashMap extends Byte2BooleanOpenCustomH
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -1267,19 +1277,19 @@ public class Byte2BooleanLinkedOpenCustomHashMap extends Byte2BooleanOpenCustomH
 				state = operator.applyAsBoolean(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return false;
+			if(size() <= 0) return OptionalBoolean.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalBoolean.of(values[index]);
 				index = (int)links[index];
 			}
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2BooleanOpenCustomHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.function.ByteBooleanUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2BooleanMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2BooleanMap;
 import speiger.src.collections.bytes.sets.AbstractByteSet;
@@ -36,6 +38,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -930,7 +933,7 @@ public class Byte2BooleanOpenCustomHashMap extends AbstractByte2BooleanMap imple
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -947,25 +950,25 @@ public class Byte2BooleanOpenCustomHashMap extends AbstractByte2BooleanMap imple
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1139,7 +1142,7 @@ public class Byte2BooleanOpenCustomHashMap extends AbstractByte2BooleanMap imple
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1156,18 +1159,18 @@ public class Byte2BooleanOpenCustomHashMap extends AbstractByte2BooleanMap imple
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1282,7 +1285,7 @@ public class Byte2BooleanOpenCustomHashMap extends AbstractByte2BooleanMap imple
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -1299,18 +1302,18 @@ public class Byte2BooleanOpenCustomHashMap extends AbstractByte2BooleanMap imple
 				}
 				state = operator.applyAsBoolean(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return false;
+			if(size() <= 0) return OptionalBoolean.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalBoolean.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return OptionalBoolean.of(values[i]);
 			}
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2ByteLinkedOpenCustomHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -13,6 +14,7 @@ import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteByteConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -664,6 +666,10 @@ public class Byte2ByteLinkedOpenCustomHashMap extends Byte2ByteOpenCustomHashMap
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ByteMap.Entry> implements Byte2ByteOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -829,7 +835,7 @@ public class Byte2ByteLinkedOpenCustomHashMap extends Byte2ByteOpenCustomHashMap
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
+		public Optional<Byte2ByteMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ByteMap.Entry state = null;
 			boolean empty = true;
@@ -844,21 +850,21 @@ public class Byte2ByteLinkedOpenCustomHashMap extends Byte2ByteOpenCustomHashMap
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry findFirst(Predicate<Byte2ByteMap.Entry> filter) {
+		public Optional<Byte2ByteMap.Entry> findFirst(Predicate<Byte2ByteMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -937,10 +943,13 @@ public class Byte2ByteLinkedOpenCustomHashMap extends Byte2ByteOpenCustomHashMap
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1083,7 +1092,7 @@ public class Byte2ByteLinkedOpenCustomHashMap extends Byte2ByteOpenCustomHashMap
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1098,19 +1107,19 @@ public class Byte2ByteLinkedOpenCustomHashMap extends Byte2ByteOpenCustomHashMap
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1245,7 +1254,7 @@ public class Byte2ByteLinkedOpenCustomHashMap extends Byte2ByteOpenCustomHashMap
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1260,19 +1269,19 @@ public class Byte2ByteLinkedOpenCustomHashMap extends Byte2ByteOpenCustomHashMap
 				state = operator.applyAsByte(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalByte.of(values[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2ByteOpenCustomHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -17,6 +18,7 @@ import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.bytes.functions.consumer.ByteByteConsumer;
 import speiger.src.collections.bytes.functions.function.ByteUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ByteMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ByteMap;
@@ -944,7 +946,7 @@ public class Byte2ByteOpenCustomHashMap extends AbstractByte2ByteMap implements
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
+		public Optional<Byte2ByteMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ByteMap.Entry state = null;
 			boolean empty = true;
@@ -961,25 +963,25 @@ public class Byte2ByteOpenCustomHashMap extends AbstractByte2ByteMap implements
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry findFirst(Predicate<Byte2ByteMap.Entry> filter) {
+		public Optional<Byte2ByteMap.Entry> findFirst(Predicate<Byte2ByteMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1153,7 +1155,7 @@ public class Byte2ByteOpenCustomHashMap extends AbstractByte2ByteMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1170,18 +1172,18 @@ public class Byte2ByteOpenCustomHashMap extends AbstractByte2ByteMap implements
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1296,7 +1298,7 @@ public class Byte2ByteOpenCustomHashMap extends AbstractByte2ByteMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1313,18 +1315,18 @@ public class Byte2ByteOpenCustomHashMap extends AbstractByte2ByteMap implements
 				}
 				state = operator.applyAsByte(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalByte.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return OptionalByte.of(values[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2CharLinkedOpenCustomHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntCharConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteCharConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -33,6 +35,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectCharConsumer;
 
 import speiger.src.collections.chars.functions.function.CharPredicate;
+import speiger.src.collections.chars.functions.OptionalChar;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.lists.ObjectListIterator;
@@ -671,6 +674,10 @@ public class Byte2CharLinkedOpenCustomHashMap extends Byte2CharOpenCustomHashMap
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2CharMap.Entry> implements Byte2CharOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -836,7 +843,7 @@ public class Byte2CharLinkedOpenCustomHashMap extends Byte2CharOpenCustomHashMap
 		}
 		
 		@Override
-		public Byte2CharMap.Entry reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
+		public Optional<Byte2CharMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2CharMap.Entry state = null;
 			boolean empty = true;
@@ -851,21 +858,21 @@ public class Byte2CharLinkedOpenCustomHashMap extends Byte2CharOpenCustomHashMap
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2CharMap.Entry findFirst(Predicate<Byte2CharMap.Entry> filter) {
+		public Optional<Byte2CharMap.Entry> findFirst(Predicate<Byte2CharMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -944,10 +951,13 @@ public class Byte2CharLinkedOpenCustomHashMap extends Byte2CharOpenCustomHashMap
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1090,7 +1100,7 @@ public class Byte2CharLinkedOpenCustomHashMap extends Byte2CharOpenCustomHashMap
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1105,19 +1115,19 @@ public class Byte2CharLinkedOpenCustomHashMap extends Byte2CharOpenCustomHashMap
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1252,7 +1262,7 @@ public class Byte2CharLinkedOpenCustomHashMap extends Byte2CharOpenCustomHashMap
 		}
 		
 		@Override
-		public char reduce(CharCharUnaryOperator operator) {
+		public OptionalChar reduce(CharCharUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			char state = (char)0;
 			boolean empty = true;
@@ -1267,19 +1277,19 @@ public class Byte2CharLinkedOpenCustomHashMap extends Byte2CharOpenCustomHashMap
 				state = operator.applyAsChar(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalChar.empty() : OptionalChar.of(state);
 		}
 		
 		@Override
-		public char findFirst(CharPredicate filter) {
+		public OptionalChar findFirst(CharPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (char)0;
+			if(size() <= 0) return OptionalChar.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalChar.of(values[index]);
 				index = (int)links[index];
 			}
-			return (char)0;
+			return OptionalChar.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2CharOpenCustomHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteCharConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2CharFunction;
 import speiger.src.collections.bytes.functions.function.ByteCharUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2CharMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2CharMap;
@@ -37,6 +39,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectCharConsumer;
 
 import speiger.src.collections.chars.functions.function.CharPredicate;
+import speiger.src.collections.chars.functions.OptionalChar;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -952,7 +955,7 @@ public class Byte2CharOpenCustomHashMap extends AbstractByte2CharMap implements
 		}
 		
 		@Override
-		public Byte2CharMap.Entry reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
+		public Optional<Byte2CharMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2CharMap.Entry state = null;
 			boolean empty = true;
@@ -969,25 +972,25 @@ public class Byte2CharOpenCustomHashMap extends AbstractByte2CharMap implements
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2CharMap.Entry findFirst(Predicate<Byte2CharMap.Entry> filter) {
+		public Optional<Byte2CharMap.Entry> findFirst(Predicate<Byte2CharMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1161,7 +1164,7 @@ public class Byte2CharOpenCustomHashMap extends AbstractByte2CharMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1178,18 +1181,18 @@ public class Byte2CharOpenCustomHashMap extends AbstractByte2CharMap implements
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1304,7 +1307,7 @@ public class Byte2CharOpenCustomHashMap extends AbstractByte2CharMap implements
 		}
 		
 		@Override
-		public char reduce(CharCharUnaryOperator operator) {
+		public OptionalChar reduce(CharCharUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			char state = (char)0;
 			boolean empty = true;
@@ -1321,18 +1324,18 @@ public class Byte2CharOpenCustomHashMap extends AbstractByte2CharMap implements
 				}
 				state = operator.applyAsChar(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalChar.empty() : OptionalChar.of(state);
 		}
 		
 		@Override
-		public char findFirst(CharPredicate filter) {
+		public OptionalChar findFirst(CharPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (char)0;
+			if(size() <= 0) return OptionalChar.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalChar.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return OptionalChar.of(values[i]);
 			}
-			return (char)0;
+			return OptionalChar.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2DoubleLinkedOpenCustomHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.DoublePredicate;
+import java.util.OptionalDouble;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntDoubleConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteDoubleConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -671,6 +674,10 @@ public class Byte2DoubleLinkedOpenCustomHashMap extends Byte2DoubleOpenCustomHas
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2DoubleMap.Entry> implements Byte2DoubleOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -836,7 +843,7 @@ public class Byte2DoubleLinkedOpenCustomHashMap extends Byte2DoubleOpenCustomHas
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
+		public Optional<Byte2DoubleMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2DoubleMap.Entry state = null;
 			boolean empty = true;
@@ -851,21 +858,21 @@ public class Byte2DoubleLinkedOpenCustomHashMap extends Byte2DoubleOpenCustomHas
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
+		public Optional<Byte2DoubleMap.Entry> findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -944,10 +951,13 @@ public class Byte2DoubleLinkedOpenCustomHashMap extends Byte2DoubleOpenCustomHas
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1090,7 +1100,7 @@ public class Byte2DoubleLinkedOpenCustomHashMap extends Byte2DoubleOpenCustomHas
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1105,19 +1115,19 @@ public class Byte2DoubleLinkedOpenCustomHashMap extends Byte2DoubleOpenCustomHas
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1252,7 +1262,7 @@ public class Byte2DoubleLinkedOpenCustomHashMap extends Byte2DoubleOpenCustomHas
 		}
 		
 		@Override
-		public double reduce(DoubleDoubleUnaryOperator operator) {
+		public OptionalDouble reduce(DoubleDoubleUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			double state = 0D;
 			boolean empty = true;
@@ -1267,19 +1277,19 @@ public class Byte2DoubleLinkedOpenCustomHashMap extends Byte2DoubleOpenCustomHas
 				state = operator.applyAsDouble(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalDouble.empty() : OptionalDouble.of(state);
 		}
 		
 		@Override
-		public double findFirst(DoublePredicate filter) {
+		public OptionalDouble findFirst(DoublePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0D;
+			if(size() <= 0) return OptionalDouble.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalDouble.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0D;
+			return OptionalDouble.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2DoubleOpenCustomHashMap.java

@@ -5,10 +5,12 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.DoublePredicate;
+import java.util.OptionalDouble;
 
 import speiger.src.collections.bytes.collections.ByteIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteDoubleConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2DoubleFunction;
 import speiger.src.collections.bytes.functions.function.ByteDoubleUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2DoubleMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2DoubleMap;
@@ -952,7 +955,7 @@ public class Byte2DoubleOpenCustomHashMap extends AbstractByte2DoubleMap impleme
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
+		public Optional<Byte2DoubleMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2DoubleMap.Entry state = null;
 			boolean empty = true;
@@ -969,25 +972,25 @@ public class Byte2DoubleOpenCustomHashMap extends AbstractByte2DoubleMap impleme
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
+		public Optional<Byte2DoubleMap.Entry> findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1161,7 +1164,7 @@ public class Byte2DoubleOpenCustomHashMap extends AbstractByte2DoubleMap impleme
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1178,18 +1181,18 @@ public class Byte2DoubleOpenCustomHashMap extends AbstractByte2DoubleMap impleme
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1304,7 +1307,7 @@ public class Byte2DoubleOpenCustomHashMap extends AbstractByte2DoubleMap impleme
 		}
 		
 		@Override
-		public double reduce(DoubleDoubleUnaryOperator operator) {
+		public OptionalDouble reduce(DoubleDoubleUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			double state = 0D;
 			boolean empty = true;
@@ -1321,18 +1324,18 @@ public class Byte2DoubleOpenCustomHashMap extends AbstractByte2DoubleMap impleme
 				}
 				state = operator.applyAsDouble(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalDouble.empty() : OptionalDouble.of(state);
 		}
 		
 		@Override
-		public double findFirst(DoublePredicate filter) {
+		public OptionalDouble findFirst(DoublePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0D;
+			if(size() <= 0) return OptionalDouble.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalDouble.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return OptionalDouble.of(values[i]);
 			}
-			return 0D;
+			return OptionalDouble.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2FloatLinkedOpenCustomHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntFloatConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteFloatConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -33,6 +35,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectFloatConsumer;
 
 import speiger.src.collections.floats.functions.function.FloatPredicate;
+import speiger.src.collections.floats.functions.OptionalFloat;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.lists.ObjectListIterator;
@@ -671,6 +674,10 @@ public class Byte2FloatLinkedOpenCustomHashMap extends Byte2FloatOpenCustomHashM
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2FloatMap.Entry> implements Byte2FloatOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -836,7 +843,7 @@ public class Byte2FloatLinkedOpenCustomHashMap extends Byte2FloatOpenCustomHashM
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
+		public Optional<Byte2FloatMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2FloatMap.Entry state = null;
 			boolean empty = true;
@@ -851,21 +858,21 @@ public class Byte2FloatLinkedOpenCustomHashMap extends Byte2FloatOpenCustomHashM
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry findFirst(Predicate<Byte2FloatMap.Entry> filter) {
+		public Optional<Byte2FloatMap.Entry> findFirst(Predicate<Byte2FloatMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -944,10 +951,13 @@ public class Byte2FloatLinkedOpenCustomHashMap extends Byte2FloatOpenCustomHashM
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1090,7 +1100,7 @@ public class Byte2FloatLinkedOpenCustomHashMap extends Byte2FloatOpenCustomHashM
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1105,19 +1115,19 @@ public class Byte2FloatLinkedOpenCustomHashMap extends Byte2FloatOpenCustomHashM
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1252,7 +1262,7 @@ public class Byte2FloatLinkedOpenCustomHashMap extends Byte2FloatOpenCustomHashM
 		}
 		
 		@Override
-		public float reduce(FloatFloatUnaryOperator operator) {
+		public OptionalFloat reduce(FloatFloatUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			float state = 0F;
 			boolean empty = true;
@@ -1267,19 +1277,19 @@ public class Byte2FloatLinkedOpenCustomHashMap extends Byte2FloatOpenCustomHashM
 				state = operator.applyAsFloat(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalFloat.empty() : OptionalFloat.of(state);
 		}
 		
 		@Override
-		public float findFirst(FloatPredicate filter) {
+		public OptionalFloat findFirst(FloatPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0F;
+			if(size() <= 0) return OptionalFloat.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalFloat.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0F;
+			return OptionalFloat.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2FloatOpenCustomHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteFloatConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2FloatFunction;
 import speiger.src.collections.bytes.functions.function.ByteFloatUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2FloatMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2FloatMap;
@@ -37,6 +39,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectFloatConsumer;
 
 import speiger.src.collections.floats.functions.function.FloatPredicate;
+import speiger.src.collections.floats.functions.OptionalFloat;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -952,7 +955,7 @@ public class Byte2FloatOpenCustomHashMap extends AbstractByte2FloatMap implement
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
+		public Optional<Byte2FloatMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2FloatMap.Entry state = null;
 			boolean empty = true;
@@ -969,25 +972,25 @@ public class Byte2FloatOpenCustomHashMap extends AbstractByte2FloatMap implement
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry findFirst(Predicate<Byte2FloatMap.Entry> filter) {
+		public Optional<Byte2FloatMap.Entry> findFirst(Predicate<Byte2FloatMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1161,7 +1164,7 @@ public class Byte2FloatOpenCustomHashMap extends AbstractByte2FloatMap implement
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1178,18 +1181,18 @@ public class Byte2FloatOpenCustomHashMap extends AbstractByte2FloatMap implement
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1304,7 +1307,7 @@ public class Byte2FloatOpenCustomHashMap extends AbstractByte2FloatMap implement
 		}
 		
 		@Override
-		public float reduce(FloatFloatUnaryOperator operator) {
+		public OptionalFloat reduce(FloatFloatUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			float state = 0F;
 			boolean empty = true;
@@ -1321,18 +1324,18 @@ public class Byte2FloatOpenCustomHashMap extends AbstractByte2FloatMap implement
 				}
 				state = operator.applyAsFloat(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalFloat.empty() : OptionalFloat.of(state);
 		}
 		
 		@Override
-		public float findFirst(FloatPredicate filter) {
+		public OptionalFloat findFirst(FloatPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0F;
+			if(size() <= 0) return OptionalFloat.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalFloat.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return OptionalFloat.of(values[i]);
 			}
-			return 0F;
+			return OptionalFloat.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2IntLinkedOpenCustomHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.IntPredicate;
+import java.util.OptionalInt;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntIntConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteIntConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -671,6 +674,10 @@ public class Byte2IntLinkedOpenCustomHashMap extends Byte2IntOpenCustomHashMap i
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2IntMap.Entry> implements Byte2IntOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -836,7 +843,7 @@ public class Byte2IntLinkedOpenCustomHashMap extends Byte2IntOpenCustomHashMap i
 		}
 		
 		@Override
-		public Byte2IntMap.Entry reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
+		public Optional<Byte2IntMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2IntMap.Entry state = null;
 			boolean empty = true;
@@ -851,21 +858,21 @@ public class Byte2IntLinkedOpenCustomHashMap extends Byte2IntOpenCustomHashMap i
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2IntMap.Entry findFirst(Predicate<Byte2IntMap.Entry> filter) {
+		public Optional<Byte2IntMap.Entry> findFirst(Predicate<Byte2IntMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -944,10 +951,13 @@ public class Byte2IntLinkedOpenCustomHashMap extends Byte2IntOpenCustomHashMap i
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1090,7 +1100,7 @@ public class Byte2IntLinkedOpenCustomHashMap extends Byte2IntOpenCustomHashMap i
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1105,19 +1115,19 @@ public class Byte2IntLinkedOpenCustomHashMap extends Byte2IntOpenCustomHashMap i
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1252,7 +1262,7 @@ public class Byte2IntLinkedOpenCustomHashMap extends Byte2IntOpenCustomHashMap i
 		}
 		
 		@Override
-		public int reduce(IntIntUnaryOperator operator) {
+		public OptionalInt reduce(IntIntUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			int state = 0;
 			boolean empty = true;
@@ -1267,19 +1277,19 @@ public class Byte2IntLinkedOpenCustomHashMap extends Byte2IntOpenCustomHashMap i
 				state = operator.applyAsInt(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalInt.empty() : OptionalInt.of(state);
 		}
 		
 		@Override
-		public int findFirst(IntPredicate filter) {
+		public OptionalInt findFirst(IntPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0;
+			if(size() <= 0) return OptionalInt.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalInt.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0;
+			return OptionalInt.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2IntOpenCustomHashMap.java

@@ -5,10 +5,12 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.IntPredicate;
+import java.util.OptionalInt;
 
 import speiger.src.collections.bytes.collections.ByteIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteIntConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2IntFunction;
 import speiger.src.collections.bytes.functions.function.ByteIntUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2IntMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2IntMap;
@@ -952,7 +955,7 @@ public class Byte2IntOpenCustomHashMap extends AbstractByte2IntMap implements IT
 		}
 		
 		@Override
-		public Byte2IntMap.Entry reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
+		public Optional<Byte2IntMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2IntMap.Entry state = null;
 			boolean empty = true;
@@ -969,25 +972,25 @@ public class Byte2IntOpenCustomHashMap extends AbstractByte2IntMap implements IT
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2IntMap.Entry findFirst(Predicate<Byte2IntMap.Entry> filter) {
+		public Optional<Byte2IntMap.Entry> findFirst(Predicate<Byte2IntMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1161,7 +1164,7 @@ public class Byte2IntOpenCustomHashMap extends AbstractByte2IntMap implements IT
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1178,18 +1181,18 @@ public class Byte2IntOpenCustomHashMap extends AbstractByte2IntMap implements IT
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1304,7 +1307,7 @@ public class Byte2IntOpenCustomHashMap extends AbstractByte2IntMap implements IT
 		}
 		
 		@Override
-		public int reduce(IntIntUnaryOperator operator) {
+		public OptionalInt reduce(IntIntUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			int state = 0;
 			boolean empty = true;
@@ -1321,18 +1324,18 @@ public class Byte2IntOpenCustomHashMap extends AbstractByte2IntMap implements IT
 				}
 				state = operator.applyAsInt(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalInt.empty() : OptionalInt.of(state);
 		}
 		
 		@Override
-		public int findFirst(IntPredicate filter) {
+		public OptionalInt findFirst(IntPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0;
+			if(size() <= 0) return OptionalInt.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalInt.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return OptionalInt.of(values[i]);
 			}
-			return 0;
+			return OptionalInt.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2LongLinkedOpenCustomHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.LongPredicate;
+import java.util.OptionalLong;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntLongConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteLongConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -671,6 +674,10 @@ public class Byte2LongLinkedOpenCustomHashMap extends Byte2LongOpenCustomHashMap
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2LongMap.Entry> implements Byte2LongOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -836,7 +843,7 @@ public class Byte2LongLinkedOpenCustomHashMap extends Byte2LongOpenCustomHashMap
 		}
 		
 		@Override
-		public Byte2LongMap.Entry reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
+		public Optional<Byte2LongMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2LongMap.Entry state = null;
 			boolean empty = true;
@@ -851,21 +858,21 @@ public class Byte2LongLinkedOpenCustomHashMap extends Byte2LongOpenCustomHashMap
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2LongMap.Entry findFirst(Predicate<Byte2LongMap.Entry> filter) {
+		public Optional<Byte2LongMap.Entry> findFirst(Predicate<Byte2LongMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -944,10 +951,13 @@ public class Byte2LongLinkedOpenCustomHashMap extends Byte2LongOpenCustomHashMap
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1090,7 +1100,7 @@ public class Byte2LongLinkedOpenCustomHashMap extends Byte2LongOpenCustomHashMap
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1105,19 +1115,19 @@ public class Byte2LongLinkedOpenCustomHashMap extends Byte2LongOpenCustomHashMap
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1252,7 +1262,7 @@ public class Byte2LongLinkedOpenCustomHashMap extends Byte2LongOpenCustomHashMap
 		}
 		
 		@Override
-		public long reduce(LongLongUnaryOperator operator) {
+		public OptionalLong reduce(LongLongUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			long state = 0L;
 			boolean empty = true;
@@ -1267,19 +1277,19 @@ public class Byte2LongLinkedOpenCustomHashMap extends Byte2LongOpenCustomHashMap
 				state = operator.applyAsLong(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalLong.empty() : OptionalLong.of(state);
 		}
 		
 		@Override
-		public long findFirst(LongPredicate filter) {
+		public OptionalLong findFirst(LongPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0L;
+			if(size() <= 0) return OptionalLong.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalLong.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0L;
+			return OptionalLong.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2LongOpenCustomHashMap.java

@@ -5,10 +5,12 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.LongPredicate;
+import java.util.OptionalLong;
 
 import speiger.src.collections.bytes.collections.ByteIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteLongConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2LongFunction;
 import speiger.src.collections.bytes.functions.function.ByteLongUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2LongMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2LongMap;
@@ -952,7 +955,7 @@ public class Byte2LongOpenCustomHashMap extends AbstractByte2LongMap implements
 		}
 		
 		@Override
-		public Byte2LongMap.Entry reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
+		public Optional<Byte2LongMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2LongMap.Entry state = null;
 			boolean empty = true;
@@ -969,25 +972,25 @@ public class Byte2LongOpenCustomHashMap extends AbstractByte2LongMap implements
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2LongMap.Entry findFirst(Predicate<Byte2LongMap.Entry> filter) {
+		public Optional<Byte2LongMap.Entry> findFirst(Predicate<Byte2LongMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1161,7 +1164,7 @@ public class Byte2LongOpenCustomHashMap extends AbstractByte2LongMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1178,18 +1181,18 @@ public class Byte2LongOpenCustomHashMap extends AbstractByte2LongMap implements
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1304,7 +1307,7 @@ public class Byte2LongOpenCustomHashMap extends AbstractByte2LongMap implements
 		}
 		
 		@Override
-		public long reduce(LongLongUnaryOperator operator) {
+		public OptionalLong reduce(LongLongUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			long state = 0L;
 			boolean empty = true;
@@ -1321,18 +1324,18 @@ public class Byte2LongOpenCustomHashMap extends AbstractByte2LongMap implements
 				}
 				state = operator.applyAsLong(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalLong.empty() : OptionalLong.of(state);
 		}
 		
 		@Override
-		public long findFirst(LongPredicate filter) {
+		public OptionalLong findFirst(LongPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0L;
+			if(size() <= 0) return OptionalLong.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalLong.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return OptionalLong.of(values[i]);
 			}
-			return 0L;
+			return OptionalLong.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2ObjectLinkedOpenCustomHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -13,6 +14,7 @@ import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteObjectConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -666,6 +668,10 @@ public class Byte2ObjectLinkedOpenCustomHashMap<V> extends Byte2ObjectOpenCustom
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ObjectMap.Entry<V>> implements Byte2ObjectOrderedMap.FastOrderedSet<V> {
+		@Override
+		public void addFirst(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -831,7 +837,7 @@ public class Byte2ObjectLinkedOpenCustomHashMap<V> extends Byte2ObjectOpenCustom
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
+		public Optional<Byte2ObjectMap.Entry<V>> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ObjectMap.Entry<V> state = null;
 			boolean empty = true;
@@ -846,21 +852,21 @@ public class Byte2ObjectLinkedOpenCustomHashMap<V> extends Byte2ObjectOpenCustom
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
+		public Optional<Byte2ObjectMap.Entry<V>> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -939,10 +945,13 @@ public class Byte2ObjectLinkedOpenCustomHashMap<V> extends Byte2ObjectOpenCustom
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1085,7 +1094,7 @@ public class Byte2ObjectLinkedOpenCustomHashMap<V> extends Byte2ObjectOpenCustom
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1100,19 +1109,19 @@ public class Byte2ObjectLinkedOpenCustomHashMap<V> extends Byte2ObjectOpenCustom
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1257,7 @@ public class Byte2ObjectLinkedOpenCustomHashMap<V> extends Byte2ObjectOpenCustom
 		}
 		
 		@Override
-		public V reduce(ObjectObjectUnaryOperator<V, V> operator) {
+		public Optional<V> reduce(ObjectObjectUnaryOperator<V, V> operator) {
 			Objects.requireNonNull(operator);
 			V state = null;
 			boolean empty = true;
@@ -1263,19 +1272,19 @@ public class Byte2ObjectLinkedOpenCustomHashMap<V> extends Byte2ObjectOpenCustom
 				state = operator.apply(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public V findFirst(Predicate<V> filter) {
+		public Optional<V> findFirst(Predicate<V> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return Optional.ofNullable(values[index]);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2ObjectOpenCustomHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -18,6 +19,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteObjectConsumer;
 import speiger.src.collections.bytes.functions.function.ByteFunction;
 import speiger.src.collections.bytes.functions.function.ByteObjectUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ObjectMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ObjectMap;
@@ -868,7 +870,7 @@ public class Byte2ObjectOpenCustomHashMap<V> extends AbstractByte2ObjectMap<V> i
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
+		public Optional<Byte2ObjectMap.Entry<V>> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ObjectMap.Entry<V> state = null;
 			boolean empty = true;
@@ -885,25 +887,25 @@ public class Byte2ObjectOpenCustomHashMap<V> extends AbstractByte2ObjectMap<V> i
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
+		public Optional<Byte2ObjectMap.Entry<V>> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1077,7 +1079,7 @@ public class Byte2ObjectOpenCustomHashMap<V> extends AbstractByte2ObjectMap<V> i
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1094,18 +1096,18 @@ public class Byte2ObjectOpenCustomHashMap<V> extends AbstractByte2ObjectMap<V> i
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1220,7 +1222,7 @@ public class Byte2ObjectOpenCustomHashMap<V> extends AbstractByte2ObjectMap<V> i
 		}
 		
 		@Override
-		public V reduce(ObjectObjectUnaryOperator<V, V> operator) {
+		public Optional<V> reduce(ObjectObjectUnaryOperator<V, V> operator) {
 			Objects.requireNonNull(operator);
 			V state = null;
 			boolean empty = true;
@@ -1237,18 +1239,18 @@ public class Byte2ObjectOpenCustomHashMap<V> extends AbstractByte2ObjectMap<V> i
 				}
 				state = operator.apply(state, values[i]);
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public V findFirst(Predicate<V> filter) {
+		public Optional<V> findFirst(Predicate<V> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return Optional.ofNullable(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return Optional.ofNullable(values[i]);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2ShortLinkedOpenCustomHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntShortConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteShortConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -33,6 +35,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectShortConsumer;
 
 import speiger.src.collections.shorts.functions.function.ShortPredicate;
+import speiger.src.collections.shorts.functions.OptionalShort;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.lists.ObjectListIterator;
@@ -671,6 +674,10 @@ public class Byte2ShortLinkedOpenCustomHashMap extends Byte2ShortOpenCustomHashM
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ShortMap.Entry> implements Byte2ShortOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -836,7 +843,7 @@ public class Byte2ShortLinkedOpenCustomHashMap extends Byte2ShortOpenCustomHashM
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
+		public Optional<Byte2ShortMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ShortMap.Entry state = null;
 			boolean empty = true;
@@ -851,21 +858,21 @@ public class Byte2ShortLinkedOpenCustomHashMap extends Byte2ShortOpenCustomHashM
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry findFirst(Predicate<Byte2ShortMap.Entry> filter) {
+		public Optional<Byte2ShortMap.Entry> findFirst(Predicate<Byte2ShortMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -944,10 +951,13 @@ public class Byte2ShortLinkedOpenCustomHashMap extends Byte2ShortOpenCustomHashM
 		public boolean add(byte o) {
 			throw new UnsupportedOperationException();
 		}
-		
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
-
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
 
@@ -1090,7 +1100,7 @@ public class Byte2ShortLinkedOpenCustomHashMap extends Byte2ShortOpenCustomHashM
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1105,19 +1115,19 @@ public class Byte2ShortLinkedOpenCustomHashMap extends Byte2ShortOpenCustomHashM
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1252,7 +1262,7 @@ public class Byte2ShortLinkedOpenCustomHashMap extends Byte2ShortOpenCustomHashM
 		}
 		
 		@Override
-		public short reduce(ShortShortUnaryOperator operator) {
+		public OptionalShort reduce(ShortShortUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			short state = (short)0;
 			boolean empty = true;
@@ -1267,19 +1277,19 @@ public class Byte2ShortLinkedOpenCustomHashMap extends Byte2ShortOpenCustomHashM
 				state = operator.applyAsShort(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalShort.empty() : OptionalShort.of(state);
 		}
 		
 		@Override
-		public short findFirst(ShortPredicate filter) {
+		public OptionalShort findFirst(ShortPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (short)0;
+			if(size() <= 0) return OptionalShort.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalShort.of(values[index]);
 				index = (int)links[index];
 			}
-			return (short)0;
+			return OptionalShort.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/customHash/Byte2ShortOpenCustomHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteShortConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2ShortFunction;
 import speiger.src.collections.bytes.functions.function.ByteShortUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ShortMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ShortMap;
@@ -37,6 +39,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectShortConsumer;
 
 import speiger.src.collections.shorts.functions.function.ShortPredicate;
+import speiger.src.collections.shorts.functions.OptionalShort;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -952,7 +955,7 @@ public class Byte2ShortOpenCustomHashMap extends AbstractByte2ShortMap implement
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
+		public Optional<Byte2ShortMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ShortMap.Entry state = null;
 			boolean empty = true;
@@ -969,25 +972,25 @@ public class Byte2ShortOpenCustomHashMap extends AbstractByte2ShortMap implement
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry findFirst(Predicate<Byte2ShortMap.Entry> filter) {
+		public Optional<Byte2ShortMap.Entry> findFirst(Predicate<Byte2ShortMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(!strategy.equals(keys[i], (byte)0)) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1161,7 +1164,7 @@ public class Byte2ShortOpenCustomHashMap extends AbstractByte2ShortMap implement
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1178,18 +1181,18 @@ public class Byte2ShortOpenCustomHashMap extends AbstractByte2ShortMap implement
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return keys[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1304,7 +1307,7 @@ public class Byte2ShortOpenCustomHashMap extends AbstractByte2ShortMap implement
 		}
 		
 		@Override
-		public short reduce(ShortShortUnaryOperator operator) {
+		public OptionalShort reduce(ShortShortUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			short state = (short)0;
 			boolean empty = true;
@@ -1321,18 +1324,18 @@ public class Byte2ShortOpenCustomHashMap extends AbstractByte2ShortMap implement
 				}
 				state = operator.applyAsShort(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalShort.empty() : OptionalShort.of(state);
 		}
 		
 		@Override
-		public short findFirst(ShortPredicate filter) {
+		public OptionalShort findFirst(ShortPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (short)0;
+			if(size() <= 0) return OptionalShort.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalShort.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return values[i];
+				if(!strategy.equals(keys[i], (byte)0) && filter.test(values[i])) return OptionalShort.of(values[i]);
 			}
-			return (short)0;
+			return OptionalShort.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2BooleanLinkedOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -32,6 +34,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.lists.ObjectListIterator;
@@ -669,6 +672,10 @@ public class Byte2BooleanLinkedOpenHashMap extends Byte2BooleanOpenHashMap imple
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2BooleanMap.Entry> implements Byte2BooleanOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -834,7 +841,7 @@ public class Byte2BooleanLinkedOpenHashMap extends Byte2BooleanOpenHashMap imple
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -849,21 +856,21 @@ public class Byte2BooleanLinkedOpenHashMap extends Byte2BooleanOpenHashMap imple
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -939,6 +946,12 @@ public class Byte2BooleanLinkedOpenHashMap extends Byte2BooleanOpenHashMap imple
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1085,7 +1098,7 @@ public class Byte2BooleanLinkedOpenHashMap extends Byte2BooleanOpenHashMap imple
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1100,19 +1113,19 @@ public class Byte2BooleanLinkedOpenHashMap extends Byte2BooleanOpenHashMap imple
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1261,7 @@ public class Byte2BooleanLinkedOpenHashMap extends Byte2BooleanOpenHashMap imple
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -1263,19 +1276,19 @@ public class Byte2BooleanLinkedOpenHashMap extends Byte2BooleanOpenHashMap imple
 				state = operator.applyAsBoolean(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return false;
+			if(size() <= 0) return OptionalBoolean.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalBoolean.of(values[index]);
 				index = (int)links[index];
 			}
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2BooleanOpenHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.function.ByteBooleanUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2BooleanMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2BooleanMap;
 import speiger.src.collections.bytes.sets.AbstractByteSet;
@@ -33,6 +35,7 @@ import speiger.src.collections.booleans.functions.BooleanConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -898,7 +901,7 @@ public class Byte2BooleanOpenHashMap extends AbstractByte2BooleanMap implements
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -915,25 +918,25 @@ public class Byte2BooleanOpenHashMap extends AbstractByte2BooleanMap implements
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1105,7 +1108,7 @@ public class Byte2BooleanOpenHashMap extends AbstractByte2BooleanMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1122,18 +1125,18 @@ public class Byte2BooleanOpenHashMap extends AbstractByte2BooleanMap implements
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1251,7 @@ public class Byte2BooleanOpenHashMap extends AbstractByte2BooleanMap implements
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -1265,18 +1268,18 @@ public class Byte2BooleanOpenHashMap extends AbstractByte2BooleanMap implements
 				}
 				state = operator.applyAsBoolean(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return false;
+			if(size() <= 0) return OptionalBoolean.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalBoolean.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return OptionalBoolean.of(values[i]);
 			}
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2ByteLinkedOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -13,6 +14,7 @@ import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteByteConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -662,6 +664,10 @@ public class Byte2ByteLinkedOpenHashMap extends Byte2ByteOpenHashMap implements
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ByteMap.Entry> implements Byte2ByteOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -827,7 +833,7 @@ public class Byte2ByteLinkedOpenHashMap extends Byte2ByteOpenHashMap implements
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
+		public Optional<Byte2ByteMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ByteMap.Entry state = null;
 			boolean empty = true;
@@ -842,21 +848,21 @@ public class Byte2ByteLinkedOpenHashMap extends Byte2ByteOpenHashMap implements
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry findFirst(Predicate<Byte2ByteMap.Entry> filter) {
+		public Optional<Byte2ByteMap.Entry> findFirst(Predicate<Byte2ByteMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -932,6 +938,12 @@ public class Byte2ByteLinkedOpenHashMap extends Byte2ByteOpenHashMap implements
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1078,7 +1090,7 @@ public class Byte2ByteLinkedOpenHashMap extends Byte2ByteOpenHashMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1093,19 +1105,19 @@ public class Byte2ByteLinkedOpenHashMap extends Byte2ByteOpenHashMap implements
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1241,7 +1253,7 @@ public class Byte2ByteLinkedOpenHashMap extends Byte2ByteOpenHashMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1256,19 +1268,19 @@ public class Byte2ByteLinkedOpenHashMap extends Byte2ByteOpenHashMap implements
 				state = operator.applyAsByte(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalByte.of(values[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2ByteOpenHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -17,6 +18,7 @@ import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.bytes.functions.consumer.ByteByteConsumer;
 import speiger.src.collections.bytes.functions.function.ByteUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ByteMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ByteMap;
@@ -914,7 +916,7 @@ public class Byte2ByteOpenHashMap extends AbstractByte2ByteMap implements ITrimm
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
+		public Optional<Byte2ByteMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ByteMap.Entry state = null;
 			boolean empty = true;
@@ -931,25 +933,25 @@ public class Byte2ByteOpenHashMap extends AbstractByte2ByteMap implements ITrimm
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry findFirst(Predicate<Byte2ByteMap.Entry> filter) {
+		public Optional<Byte2ByteMap.Entry> findFirst(Predicate<Byte2ByteMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1121,7 +1123,7 @@ public class Byte2ByteOpenHashMap extends AbstractByte2ByteMap implements ITrimm
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1138,18 +1140,18 @@ public class Byte2ByteOpenHashMap extends AbstractByte2ByteMap implements ITrimm
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1264,7 +1266,7 @@ public class Byte2ByteOpenHashMap extends AbstractByte2ByteMap implements ITrimm
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1281,18 +1283,18 @@ public class Byte2ByteOpenHashMap extends AbstractByte2ByteMap implements ITrimm
 				}
 				state = operator.applyAsByte(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalByte.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return OptionalByte.of(values[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2CharLinkedOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntCharConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteCharConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -32,6 +34,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectCharConsumer;
 
 import speiger.src.collections.chars.functions.function.CharPredicate;
+import speiger.src.collections.chars.functions.OptionalChar;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.lists.ObjectListIterator;
@@ -669,6 +672,10 @@ public class Byte2CharLinkedOpenHashMap extends Byte2CharOpenHashMap implements
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2CharMap.Entry> implements Byte2CharOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -834,7 +841,7 @@ public class Byte2CharLinkedOpenHashMap extends Byte2CharOpenHashMap implements
 		}
 		
 		@Override
-		public Byte2CharMap.Entry reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
+		public Optional<Byte2CharMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2CharMap.Entry state = null;
 			boolean empty = true;
@@ -849,21 +856,21 @@ public class Byte2CharLinkedOpenHashMap extends Byte2CharOpenHashMap implements
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2CharMap.Entry findFirst(Predicate<Byte2CharMap.Entry> filter) {
+		public Optional<Byte2CharMap.Entry> findFirst(Predicate<Byte2CharMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -939,6 +946,12 @@ public class Byte2CharLinkedOpenHashMap extends Byte2CharOpenHashMap implements
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1085,7 +1098,7 @@ public class Byte2CharLinkedOpenHashMap extends Byte2CharOpenHashMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1100,19 +1113,19 @@ public class Byte2CharLinkedOpenHashMap extends Byte2CharOpenHashMap implements
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1261,7 @@ public class Byte2CharLinkedOpenHashMap extends Byte2CharOpenHashMap implements
 		}
 		
 		@Override
-		public char reduce(CharCharUnaryOperator operator) {
+		public OptionalChar reduce(CharCharUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			char state = (char)0;
 			boolean empty = true;
@@ -1263,19 +1276,19 @@ public class Byte2CharLinkedOpenHashMap extends Byte2CharOpenHashMap implements
 				state = operator.applyAsChar(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalChar.empty() : OptionalChar.of(state);
 		}
 		
 		@Override
-		public char findFirst(CharPredicate filter) {
+		public OptionalChar findFirst(CharPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (char)0;
+			if(size() <= 0) return OptionalChar.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalChar.of(values[index]);
 				index = (int)links[index];
 			}
-			return (char)0;
+			return OptionalChar.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2CharOpenHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteCharConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2CharFunction;
 import speiger.src.collections.bytes.functions.function.ByteCharUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2CharMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2CharMap;
@@ -34,6 +36,7 @@ import speiger.src.collections.chars.functions.CharConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectCharConsumer;
 import speiger.src.collections.chars.functions.function.CharPredicate;
+import speiger.src.collections.chars.functions.OptionalChar;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -920,7 +923,7 @@ public class Byte2CharOpenHashMap extends AbstractByte2CharMap implements ITrimm
 		}
 		
 		@Override
-		public Byte2CharMap.Entry reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
+		public Optional<Byte2CharMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2CharMap.Entry state = null;
 			boolean empty = true;
@@ -937,25 +940,25 @@ public class Byte2CharOpenHashMap extends AbstractByte2CharMap implements ITrimm
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2CharMap.Entry findFirst(Predicate<Byte2CharMap.Entry> filter) {
+		public Optional<Byte2CharMap.Entry> findFirst(Predicate<Byte2CharMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1127,7 +1130,7 @@ public class Byte2CharOpenHashMap extends AbstractByte2CharMap implements ITrimm
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1144,18 +1147,18 @@ public class Byte2CharOpenHashMap extends AbstractByte2CharMap implements ITrimm
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1270,7 +1273,7 @@ public class Byte2CharOpenHashMap extends AbstractByte2CharMap implements ITrimm
 		}
 		
 		@Override
-		public char reduce(CharCharUnaryOperator operator) {
+		public OptionalChar reduce(CharCharUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			char state = (char)0;
 			boolean empty = true;
@@ -1287,18 +1290,18 @@ public class Byte2CharOpenHashMap extends AbstractByte2CharMap implements ITrimm
 				}
 				state = operator.applyAsChar(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalChar.empty() : OptionalChar.of(state);
 		}
 		
 		@Override
-		public char findFirst(CharPredicate filter) {
+		public OptionalChar findFirst(CharPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (char)0;
+			if(size() <= 0) return OptionalChar.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalChar.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return OptionalChar.of(values[i]);
 			}
-			return (char)0;
+			return OptionalChar.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2DoubleLinkedOpenHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.DoublePredicate;
+import java.util.OptionalDouble;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntDoubleConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteDoubleConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -669,6 +672,10 @@ public class Byte2DoubleLinkedOpenHashMap extends Byte2DoubleOpenHashMap impleme
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2DoubleMap.Entry> implements Byte2DoubleOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -834,7 +841,7 @@ public class Byte2DoubleLinkedOpenHashMap extends Byte2DoubleOpenHashMap impleme
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
+		public Optional<Byte2DoubleMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2DoubleMap.Entry state = null;
 			boolean empty = true;
@@ -849,21 +856,21 @@ public class Byte2DoubleLinkedOpenHashMap extends Byte2DoubleOpenHashMap impleme
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
+		public Optional<Byte2DoubleMap.Entry> findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -939,6 +946,12 @@ public class Byte2DoubleLinkedOpenHashMap extends Byte2DoubleOpenHashMap impleme
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1085,7 +1098,7 @@ public class Byte2DoubleLinkedOpenHashMap extends Byte2DoubleOpenHashMap impleme
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1100,19 +1113,19 @@ public class Byte2DoubleLinkedOpenHashMap extends Byte2DoubleOpenHashMap impleme
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1261,7 @@ public class Byte2DoubleLinkedOpenHashMap extends Byte2DoubleOpenHashMap impleme
 		}
 		
 		@Override
-		public double reduce(DoubleDoubleUnaryOperator operator) {
+		public OptionalDouble reduce(DoubleDoubleUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			double state = 0D;
 			boolean empty = true;
@@ -1263,19 +1276,19 @@ public class Byte2DoubleLinkedOpenHashMap extends Byte2DoubleOpenHashMap impleme
 				state = operator.applyAsDouble(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalDouble.empty() : OptionalDouble.of(state);
 		}
 		
 		@Override
-		public double findFirst(DoublePredicate filter) {
+		public OptionalDouble findFirst(DoublePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0D;
+			if(size() <= 0) return OptionalDouble.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalDouble.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0D;
+			return OptionalDouble.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2DoubleOpenHashMap.java

@@ -5,10 +5,12 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.DoublePredicate;
+import java.util.OptionalDouble;
 
 import speiger.src.collections.bytes.collections.ByteIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteDoubleConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2DoubleFunction;
 import speiger.src.collections.bytes.functions.function.ByteDoubleUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2DoubleMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2DoubleMap;
@@ -920,7 +923,7 @@ public class Byte2DoubleOpenHashMap extends AbstractByte2DoubleMap implements IT
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
+		public Optional<Byte2DoubleMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2DoubleMap.Entry state = null;
 			boolean empty = true;
@@ -937,25 +940,25 @@ public class Byte2DoubleOpenHashMap extends AbstractByte2DoubleMap implements IT
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
+		public Optional<Byte2DoubleMap.Entry> findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1127,7 +1130,7 @@ public class Byte2DoubleOpenHashMap extends AbstractByte2DoubleMap implements IT
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1144,18 +1147,18 @@ public class Byte2DoubleOpenHashMap extends AbstractByte2DoubleMap implements IT
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1270,7 +1273,7 @@ public class Byte2DoubleOpenHashMap extends AbstractByte2DoubleMap implements IT
 		}
 		
 		@Override
-		public double reduce(DoubleDoubleUnaryOperator operator) {
+		public OptionalDouble reduce(DoubleDoubleUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			double state = 0D;
 			boolean empty = true;
@@ -1287,18 +1290,18 @@ public class Byte2DoubleOpenHashMap extends AbstractByte2DoubleMap implements IT
 				}
 				state = operator.applyAsDouble(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalDouble.empty() : OptionalDouble.of(state);
 		}
 		
 		@Override
-		public double findFirst(DoublePredicate filter) {
+		public OptionalDouble findFirst(DoublePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0D;
+			if(size() <= 0) return OptionalDouble.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalDouble.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return OptionalDouble.of(values[i]);
 			}
-			return 0D;
+			return OptionalDouble.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2FloatLinkedOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntFloatConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteFloatConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -32,6 +34,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectFloatConsumer;
 
 import speiger.src.collections.floats.functions.function.FloatPredicate;
+import speiger.src.collections.floats.functions.OptionalFloat;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.lists.ObjectListIterator;
@@ -669,6 +672,10 @@ public class Byte2FloatLinkedOpenHashMap extends Byte2FloatOpenHashMap implement
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2FloatMap.Entry> implements Byte2FloatOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -834,7 +841,7 @@ public class Byte2FloatLinkedOpenHashMap extends Byte2FloatOpenHashMap implement
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
+		public Optional<Byte2FloatMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2FloatMap.Entry state = null;
 			boolean empty = true;
@@ -849,21 +856,21 @@ public class Byte2FloatLinkedOpenHashMap extends Byte2FloatOpenHashMap implement
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry findFirst(Predicate<Byte2FloatMap.Entry> filter) {
+		public Optional<Byte2FloatMap.Entry> findFirst(Predicate<Byte2FloatMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -939,6 +946,12 @@ public class Byte2FloatLinkedOpenHashMap extends Byte2FloatOpenHashMap implement
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1085,7 +1098,7 @@ public class Byte2FloatLinkedOpenHashMap extends Byte2FloatOpenHashMap implement
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1100,19 +1113,19 @@ public class Byte2FloatLinkedOpenHashMap extends Byte2FloatOpenHashMap implement
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1261,7 @@ public class Byte2FloatLinkedOpenHashMap extends Byte2FloatOpenHashMap implement
 		}
 		
 		@Override
-		public float reduce(FloatFloatUnaryOperator operator) {
+		public OptionalFloat reduce(FloatFloatUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			float state = 0F;
 			boolean empty = true;
@@ -1263,19 +1276,19 @@ public class Byte2FloatLinkedOpenHashMap extends Byte2FloatOpenHashMap implement
 				state = operator.applyAsFloat(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalFloat.empty() : OptionalFloat.of(state);
 		}
 		
 		@Override
-		public float findFirst(FloatPredicate filter) {
+		public OptionalFloat findFirst(FloatPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0F;
+			if(size() <= 0) return OptionalFloat.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalFloat.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0F;
+			return OptionalFloat.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2FloatOpenHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteFloatConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2FloatFunction;
 import speiger.src.collections.bytes.functions.function.ByteFloatUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2FloatMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2FloatMap;
@@ -34,6 +36,7 @@ import speiger.src.collections.floats.functions.FloatConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectFloatConsumer;
 import speiger.src.collections.floats.functions.function.FloatPredicate;
+import speiger.src.collections.floats.functions.OptionalFloat;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -920,7 +923,7 @@ public class Byte2FloatOpenHashMap extends AbstractByte2FloatMap implements ITri
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
+		public Optional<Byte2FloatMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2FloatMap.Entry state = null;
 			boolean empty = true;
@@ -937,25 +940,25 @@ public class Byte2FloatOpenHashMap extends AbstractByte2FloatMap implements ITri
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry findFirst(Predicate<Byte2FloatMap.Entry> filter) {
+		public Optional<Byte2FloatMap.Entry> findFirst(Predicate<Byte2FloatMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1127,7 +1130,7 @@ public class Byte2FloatOpenHashMap extends AbstractByte2FloatMap implements ITri
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1144,18 +1147,18 @@ public class Byte2FloatOpenHashMap extends AbstractByte2FloatMap implements ITri
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1270,7 +1273,7 @@ public class Byte2FloatOpenHashMap extends AbstractByte2FloatMap implements ITri
 		}
 		
 		@Override
-		public float reduce(FloatFloatUnaryOperator operator) {
+		public OptionalFloat reduce(FloatFloatUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			float state = 0F;
 			boolean empty = true;
@@ -1287,18 +1290,18 @@ public class Byte2FloatOpenHashMap extends AbstractByte2FloatMap implements ITri
 				}
 				state = operator.applyAsFloat(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalFloat.empty() : OptionalFloat.of(state);
 		}
 		
 		@Override
-		public float findFirst(FloatPredicate filter) {
+		public OptionalFloat findFirst(FloatPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0F;
+			if(size() <= 0) return OptionalFloat.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalFloat.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return OptionalFloat.of(values[i]);
 			}
-			return 0F;
+			return OptionalFloat.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2IntLinkedOpenHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.IntPredicate;
+import java.util.OptionalInt;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntIntConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteIntConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -669,6 +672,10 @@ public class Byte2IntLinkedOpenHashMap extends Byte2IntOpenHashMap implements By
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2IntMap.Entry> implements Byte2IntOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -834,7 +841,7 @@ public class Byte2IntLinkedOpenHashMap extends Byte2IntOpenHashMap implements By
 		}
 		
 		@Override
-		public Byte2IntMap.Entry reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
+		public Optional<Byte2IntMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2IntMap.Entry state = null;
 			boolean empty = true;
@@ -849,21 +856,21 @@ public class Byte2IntLinkedOpenHashMap extends Byte2IntOpenHashMap implements By
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2IntMap.Entry findFirst(Predicate<Byte2IntMap.Entry> filter) {
+		public Optional<Byte2IntMap.Entry> findFirst(Predicate<Byte2IntMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -939,6 +946,12 @@ public class Byte2IntLinkedOpenHashMap extends Byte2IntOpenHashMap implements By
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1085,7 +1098,7 @@ public class Byte2IntLinkedOpenHashMap extends Byte2IntOpenHashMap implements By
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1100,19 +1113,19 @@ public class Byte2IntLinkedOpenHashMap extends Byte2IntOpenHashMap implements By
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1261,7 @@ public class Byte2IntLinkedOpenHashMap extends Byte2IntOpenHashMap implements By
 		}
 		
 		@Override
-		public int reduce(IntIntUnaryOperator operator) {
+		public OptionalInt reduce(IntIntUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			int state = 0;
 			boolean empty = true;
@@ -1263,19 +1276,19 @@ public class Byte2IntLinkedOpenHashMap extends Byte2IntOpenHashMap implements By
 				state = operator.applyAsInt(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalInt.empty() : OptionalInt.of(state);
 		}
 		
 		@Override
-		public int findFirst(IntPredicate filter) {
+		public OptionalInt findFirst(IntPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0;
+			if(size() <= 0) return OptionalInt.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalInt.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0;
+			return OptionalInt.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2IntOpenHashMap.java

@@ -5,10 +5,12 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.IntPredicate;
+import java.util.OptionalInt;
 
 import speiger.src.collections.bytes.collections.ByteIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteIntConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2IntFunction;
 import speiger.src.collections.bytes.functions.function.ByteIntUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2IntMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2IntMap;
@@ -920,7 +923,7 @@ public class Byte2IntOpenHashMap extends AbstractByte2IntMap implements ITrimmab
 		}
 		
 		@Override
-		public Byte2IntMap.Entry reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
+		public Optional<Byte2IntMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2IntMap.Entry state = null;
 			boolean empty = true;
@@ -937,25 +940,25 @@ public class Byte2IntOpenHashMap extends AbstractByte2IntMap implements ITrimmab
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2IntMap.Entry findFirst(Predicate<Byte2IntMap.Entry> filter) {
+		public Optional<Byte2IntMap.Entry> findFirst(Predicate<Byte2IntMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1127,7 +1130,7 @@ public class Byte2IntOpenHashMap extends AbstractByte2IntMap implements ITrimmab
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1144,18 +1147,18 @@ public class Byte2IntOpenHashMap extends AbstractByte2IntMap implements ITrimmab
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1270,7 +1273,7 @@ public class Byte2IntOpenHashMap extends AbstractByte2IntMap implements ITrimmab
 		}
 		
 		@Override
-		public int reduce(IntIntUnaryOperator operator) {
+		public OptionalInt reduce(IntIntUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			int state = 0;
 			boolean empty = true;
@@ -1287,18 +1290,18 @@ public class Byte2IntOpenHashMap extends AbstractByte2IntMap implements ITrimmab
 				}
 				state = operator.applyAsInt(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalInt.empty() : OptionalInt.of(state);
 		}
 		
 		@Override
-		public int findFirst(IntPredicate filter) {
+		public OptionalInt findFirst(IntPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0;
+			if(size() <= 0) return OptionalInt.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalInt.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return OptionalInt.of(values[i]);
 			}
-			return 0;
+			return OptionalInt.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2LongLinkedOpenHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.LongPredicate;
+import java.util.OptionalLong;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntLongConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteLongConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -669,6 +672,10 @@ public class Byte2LongLinkedOpenHashMap extends Byte2LongOpenHashMap implements
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2LongMap.Entry> implements Byte2LongOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -834,7 +841,7 @@ public class Byte2LongLinkedOpenHashMap extends Byte2LongOpenHashMap implements
 		}
 		
 		@Override
-		public Byte2LongMap.Entry reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
+		public Optional<Byte2LongMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2LongMap.Entry state = null;
 			boolean empty = true;
@@ -849,21 +856,21 @@ public class Byte2LongLinkedOpenHashMap extends Byte2LongOpenHashMap implements
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2LongMap.Entry findFirst(Predicate<Byte2LongMap.Entry> filter) {
+		public Optional<Byte2LongMap.Entry> findFirst(Predicate<Byte2LongMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -939,6 +946,12 @@ public class Byte2LongLinkedOpenHashMap extends Byte2LongOpenHashMap implements
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1085,7 +1098,7 @@ public class Byte2LongLinkedOpenHashMap extends Byte2LongOpenHashMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1100,19 +1113,19 @@ public class Byte2LongLinkedOpenHashMap extends Byte2LongOpenHashMap implements
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1261,7 @@ public class Byte2LongLinkedOpenHashMap extends Byte2LongOpenHashMap implements
 		}
 		
 		@Override
-		public long reduce(LongLongUnaryOperator operator) {
+		public OptionalLong reduce(LongLongUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			long state = 0L;
 			boolean empty = true;
@@ -1263,19 +1276,19 @@ public class Byte2LongLinkedOpenHashMap extends Byte2LongOpenHashMap implements
 				state = operator.applyAsLong(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalLong.empty() : OptionalLong.of(state);
 		}
 		
 		@Override
-		public long findFirst(LongPredicate filter) {
+		public OptionalLong findFirst(LongPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0L;
+			if(size() <= 0) return OptionalLong.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalLong.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0L;
+			return OptionalLong.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2LongOpenHashMap.java

@@ -5,10 +5,12 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.LongPredicate;
+import java.util.OptionalLong;
 
 import speiger.src.collections.bytes.collections.ByteIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -20,6 +22,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteLongConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2LongFunction;
 import speiger.src.collections.bytes.functions.function.ByteLongUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2LongMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2LongMap;
@@ -920,7 +923,7 @@ public class Byte2LongOpenHashMap extends AbstractByte2LongMap implements ITrimm
 		}
 		
 		@Override
-		public Byte2LongMap.Entry reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
+		public Optional<Byte2LongMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2LongMap.Entry state = null;
 			boolean empty = true;
@@ -937,25 +940,25 @@ public class Byte2LongOpenHashMap extends AbstractByte2LongMap implements ITrimm
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2LongMap.Entry findFirst(Predicate<Byte2LongMap.Entry> filter) {
+		public Optional<Byte2LongMap.Entry> findFirst(Predicate<Byte2LongMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1127,7 +1130,7 @@ public class Byte2LongOpenHashMap extends AbstractByte2LongMap implements ITrimm
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1144,18 +1147,18 @@ public class Byte2LongOpenHashMap extends AbstractByte2LongMap implements ITrimm
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1270,7 +1273,7 @@ public class Byte2LongOpenHashMap extends AbstractByte2LongMap implements ITrimm
 		}
 		
 		@Override
-		public long reduce(LongLongUnaryOperator operator) {
+		public OptionalLong reduce(LongLongUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			long state = 0L;
 			boolean empty = true;
@@ -1287,18 +1290,18 @@ public class Byte2LongOpenHashMap extends AbstractByte2LongMap implements ITrimm
 				}
 				state = operator.applyAsLong(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalLong.empty() : OptionalLong.of(state);
 		}
 		
 		@Override
-		public long findFirst(LongPredicate filter) {
+		public OptionalLong findFirst(LongPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0L;
+			if(size() <= 0) return OptionalLong.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalLong.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return OptionalLong.of(values[i]);
 			}
-			return 0L;
+			return OptionalLong.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2ObjectLinkedOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -13,6 +14,7 @@ import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteObjectConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -653,6 +655,10 @@ public class Byte2ObjectLinkedOpenHashMap<V> extends Byte2ObjectOpenHashMap<V> i
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ObjectMap.Entry<V>> implements Byte2ObjectOrderedMap.FastOrderedSet<V> {
+		@Override
+		public void addFirst(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -818,7 +824,7 @@ public class Byte2ObjectLinkedOpenHashMap<V> extends Byte2ObjectOpenHashMap<V> i
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
+		public Optional<Byte2ObjectMap.Entry<V>> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ObjectMap.Entry<V> state = null;
 			boolean empty = true;
@@ -833,21 +839,21 @@ public class Byte2ObjectLinkedOpenHashMap<V> extends Byte2ObjectOpenHashMap<V> i
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
+		public Optional<Byte2ObjectMap.Entry<V>> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -923,6 +929,12 @@ public class Byte2ObjectLinkedOpenHashMap<V> extends Byte2ObjectOpenHashMap<V> i
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1069,7 +1081,7 @@ public class Byte2ObjectLinkedOpenHashMap<V> extends Byte2ObjectOpenHashMap<V> i
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1084,19 +1096,19 @@ public class Byte2ObjectLinkedOpenHashMap<V> extends Byte2ObjectOpenHashMap<V> i
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1233,7 +1245,7 @@ public class Byte2ObjectLinkedOpenHashMap<V> extends Byte2ObjectOpenHashMap<V> i
 		}
 		
 		@Override
-		public V reduce(ObjectObjectUnaryOperator<V, V> operator) {
+		public Optional<V> reduce(ObjectObjectUnaryOperator<V, V> operator) {
 			Objects.requireNonNull(operator);
 			V state = null;
 			boolean empty = true;
@@ -1248,19 +1260,19 @@ public class Byte2ObjectLinkedOpenHashMap<V> extends Byte2ObjectOpenHashMap<V> i
 				state = operator.apply(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public V findFirst(Predicate<V> filter) {
+		public Optional<V> findFirst(Predicate<V> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return Optional.ofNullable(values[index]);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2ObjectOpenHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -18,6 +19,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteObjectConsumer;
 import speiger.src.collections.bytes.functions.function.ByteFunction;
 import speiger.src.collections.bytes.functions.function.ByteObjectUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ObjectMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ObjectMap;
@@ -837,7 +839,7 @@ public class Byte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V> impleme
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
+		public Optional<Byte2ObjectMap.Entry<V>> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ObjectMap.Entry<V> state = null;
 			boolean empty = true;
@@ -854,25 +856,25 @@ public class Byte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V> impleme
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
+		public Optional<Byte2ObjectMap.Entry<V>> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1044,7 +1046,7 @@ public class Byte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V> impleme
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1061,18 +1063,18 @@ public class Byte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V> impleme
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1187,7 +1189,7 @@ public class Byte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V> impleme
 		}
 		
 		@Override
-		public V reduce(ObjectObjectUnaryOperator<V, V> operator) {
+		public Optional<V> reduce(ObjectObjectUnaryOperator<V, V> operator) {
 			Objects.requireNonNull(operator);
 			V state = null;
 			boolean empty = true;
@@ -1204,18 +1206,18 @@ public class Byte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V> impleme
 				}
 				state = operator.apply(state, values[i]);
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public V findFirst(Predicate<V> filter) {
+		public Optional<V> findFirst(Predicate<V> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return Optional.ofNullable(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return Optional.ofNullable(values[i]);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2ShortLinkedOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntShortConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteShortConsumer;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
@@ -32,6 +34,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectShortConsumer;
 
 import speiger.src.collections.shorts.functions.function.ShortPredicate;
+import speiger.src.collections.shorts.functions.OptionalShort;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.lists.ObjectListIterator;
@@ -669,6 +672,10 @@ public class Byte2ShortLinkedOpenHashMap extends Byte2ShortOpenHashMap implement
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ShortMap.Entry> implements Byte2ShortOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -834,7 +841,7 @@ public class Byte2ShortLinkedOpenHashMap extends Byte2ShortOpenHashMap implement
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
+		public Optional<Byte2ShortMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ShortMap.Entry state = null;
 			boolean empty = true;
@@ -849,21 +856,21 @@ public class Byte2ShortLinkedOpenHashMap extends Byte2ShortOpenHashMap implement
 				state = operator.apply(state, new ValueMapEntry(index));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry findFirst(Predicate<Byte2ShortMap.Entry> filter) {
+		public Optional<Byte2ShortMap.Entry> findFirst(Predicate<Byte2ShortMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(index);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -939,6 +946,12 @@ public class Byte2ShortLinkedOpenHashMap extends Byte2ShortOpenHashMap implement
 		
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
+
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
 		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
@@ -1085,7 +1098,7 @@ public class Byte2ShortLinkedOpenHashMap extends Byte2ShortOpenHashMap implement
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1100,19 +1113,19 @@ public class Byte2ShortLinkedOpenHashMap extends Byte2ShortOpenHashMap implement
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1248,7 +1261,7 @@ public class Byte2ShortLinkedOpenHashMap extends Byte2ShortOpenHashMap implement
 		}
 		
 		@Override
-		public short reduce(ShortShortUnaryOperator operator) {
+		public OptionalShort reduce(ShortShortUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			short state = (short)0;
 			boolean empty = true;
@@ -1263,19 +1276,19 @@ public class Byte2ShortLinkedOpenHashMap extends Byte2ShortOpenHashMap implement
 				state = operator.applyAsShort(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalShort.empty() : OptionalShort.of(state);
 		}
 		
 		@Override
-		public short findFirst(ShortPredicate filter) {
+		public OptionalShort findFirst(ShortPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (short)0;
+			if(size() <= 0) return OptionalShort.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalShort.of(values[index]);
 				index = (int)links[index];
 			}
-			return (short)0;
+			return OptionalShort.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/hash/Byte2ShortOpenHashMap.java

@@ -5,6 +5,7 @@ import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -19,6 +20,7 @@ import speiger.src.collections.bytes.functions.consumer.ByteShortConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2ShortFunction;
 import speiger.src.collections.bytes.functions.function.ByteShortUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2ShortMap;
 import speiger.src.collections.bytes.maps.interfaces.Byte2ShortMap;
@@ -34,6 +36,7 @@ import speiger.src.collections.shorts.functions.ShortConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectShortConsumer;
 import speiger.src.collections.shorts.functions.function.ShortPredicate;
+import speiger.src.collections.shorts.functions.OptionalShort;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.sets.AbstractObjectSet;
 import speiger.src.collections.objects.sets.ObjectSet;
@@ -920,7 +923,7 @@ public class Byte2ShortOpenHashMap extends AbstractByte2ShortMap implements ITri
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
+		public Optional<Byte2ShortMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ShortMap.Entry state = null;
 			boolean empty = true;
@@ -937,25 +940,25 @@ public class Byte2ShortOpenHashMap extends AbstractByte2ShortMap implements ITri
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry findFirst(Predicate<Byte2ShortMap.Entry> filter) {
+		public Optional<Byte2ShortMap.Entry> findFirst(Predicate<Byte2ShortMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			if(containsNull) {
 				entry.set(nullIndex);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
 			for(int i = nullIndex-1;i>=0;i--) {
 				if(keys[i] != (byte)0) {
 					entry.set(i);
-					if(filter.test(entry)) return entry;
+					if(filter.test(entry)) return Optional.ofNullable(entry);
 				}
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -1127,7 +1130,7 @@ public class Byte2ShortOpenHashMap extends AbstractByte2ShortMap implements ITri
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1144,18 +1147,18 @@ public class Byte2ShortOpenHashMap extends AbstractByte2ShortMap implements ITri
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
-			if(containsNull && filter.test(keys[nullIndex])) return keys[nullIndex];
+			if(containsNull && filter.test(keys[nullIndex])) return OptionalByte.of(keys[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(keys[i])) return keys[i];
+				if(keys[i] != (byte)0 && filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1270,7 +1273,7 @@ public class Byte2ShortOpenHashMap extends AbstractByte2ShortMap implements ITri
 		}
 		
 		@Override
-		public short reduce(ShortShortUnaryOperator operator) {
+		public OptionalShort reduce(ShortShortUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			short state = (short)0;
 			boolean empty = true;
@@ -1287,18 +1290,18 @@ public class Byte2ShortOpenHashMap extends AbstractByte2ShortMap implements ITri
 				}
 				state = operator.applyAsShort(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalShort.empty() : OptionalShort.of(state);
 		}
 		
 		@Override
-		public short findFirst(ShortPredicate filter) {
+		public OptionalShort findFirst(ShortPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (short)0;
+			if(size() <= 0) return OptionalShort.empty();
-			if(containsNull && filter.test(values[nullIndex])) return values[nullIndex];
+			if(containsNull && filter.test(values[nullIndex])) return OptionalShort.of(values[nullIndex]);
 			for(int i = nullIndex-1;i>=0;i--) {
-				if(keys[i] != (byte)0 && filter.test(values[i])) return values[i];
+				if(keys[i] != (byte)0 && filter.test(values[i])) return OptionalShort.of(values[i]);
 			}
-			return (short)0;
+			return OptionalShort.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2BooleanOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.function.ByteBooleanUnaryOperator;
@@ -28,6 +30,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.bytes.sets.AbstractByteSet;
 import speiger.src.collections.booleans.collections.AbstractBooleanCollection;
 import speiger.src.collections.booleans.collections.BooleanOrderedCollection;
@@ -533,6 +536,10 @@ public class ImmutableByte2BooleanOpenHashMap extends AbstractByte2BooleanMap im
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2BooleanMap.Entry> implements Byte2BooleanOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -686,7 +693,7 @@ public class ImmutableByte2BooleanOpenHashMap extends AbstractByte2BooleanMap im
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -701,21 +708,21 @@ public class ImmutableByte2BooleanOpenHashMap extends AbstractByte2BooleanMap im
 				state = operator.apply(state, new BasicEntry(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry entry = new BasicEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -778,6 +785,12 @@ public class ImmutableByte2BooleanOpenHashMap extends AbstractByte2BooleanMap im
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -913,7 +926,7 @@ public class ImmutableByte2BooleanOpenHashMap extends AbstractByte2BooleanMap im
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -928,19 +941,19 @@ public class ImmutableByte2BooleanOpenHashMap extends AbstractByte2BooleanMap im
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1067,7 +1080,7 @@ public class ImmutableByte2BooleanOpenHashMap extends AbstractByte2BooleanMap im
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -1082,19 +1095,19 @@ public class ImmutableByte2BooleanOpenHashMap extends AbstractByte2BooleanMap im
 				state = operator.applyAsBoolean(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return false;
+			if(size() <= 0) return OptionalBoolean.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalBoolean.of(values[index]);
 				index = (int)links[index];
 			}
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2ByteOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -13,6 +14,7 @@ import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteByteConsumer;
 import speiger.src.collections.bytes.functions.function.ByteUnaryOperator;
@@ -529,6 +531,10 @@ public class ImmutableByte2ByteOpenHashMap extends AbstractByte2ByteMap implemen
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ByteMap.Entry> implements Byte2ByteOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -682,7 +688,7 @@ public class ImmutableByte2ByteOpenHashMap extends AbstractByte2ByteMap implemen
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
+		public Optional<Byte2ByteMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ByteMap.Entry state = null;
 			boolean empty = true;
@@ -697,21 +703,21 @@ public class ImmutableByte2ByteOpenHashMap extends AbstractByte2ByteMap implemen
 				state = operator.apply(state, new BasicEntry(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry findFirst(Predicate<Byte2ByteMap.Entry> filter) {
+		public Optional<Byte2ByteMap.Entry> findFirst(Predicate<Byte2ByteMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry entry = new BasicEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -774,6 +780,12 @@ public class ImmutableByte2ByteOpenHashMap extends AbstractByte2ByteMap implemen
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -909,7 +921,7 @@ public class ImmutableByte2ByteOpenHashMap extends AbstractByte2ByteMap implemen
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -924,19 +936,19 @@ public class ImmutableByte2ByteOpenHashMap extends AbstractByte2ByteMap implemen
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1063,7 +1075,7 @@ public class ImmutableByte2ByteOpenHashMap extends AbstractByte2ByteMap implemen
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1078,19 +1090,19 @@ public class ImmutableByte2ByteOpenHashMap extends AbstractByte2ByteMap implemen
 				state = operator.applyAsByte(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalByte.of(values[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2CharOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntCharConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteCharConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2CharFunction;
@@ -29,6 +31,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectCharConsumer;
 
 import speiger.src.collections.chars.functions.function.CharPredicate;
+import speiger.src.collections.chars.functions.OptionalChar;
 import speiger.src.collections.bytes.sets.AbstractByteSet;
 import speiger.src.collections.chars.collections.AbstractCharCollection;
 import speiger.src.collections.chars.collections.CharOrderedCollection;
@@ -538,6 +541,10 @@ public class ImmutableByte2CharOpenHashMap extends AbstractByte2CharMap implemen
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2CharMap.Entry> implements Byte2CharOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -691,7 +698,7 @@ public class ImmutableByte2CharOpenHashMap extends AbstractByte2CharMap implemen
 		}
 		
 		@Override
-		public Byte2CharMap.Entry reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
+		public Optional<Byte2CharMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2CharMap.Entry state = null;
 			boolean empty = true;
@@ -706,21 +713,21 @@ public class ImmutableByte2CharOpenHashMap extends AbstractByte2CharMap implemen
 				state = operator.apply(state, new BasicEntry(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2CharMap.Entry findFirst(Predicate<Byte2CharMap.Entry> filter) {
+		public Optional<Byte2CharMap.Entry> findFirst(Predicate<Byte2CharMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry entry = new BasicEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -783,6 +790,12 @@ public class ImmutableByte2CharOpenHashMap extends AbstractByte2CharMap implemen
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -918,7 +931,7 @@ public class ImmutableByte2CharOpenHashMap extends AbstractByte2CharMap implemen
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -933,19 +946,19 @@ public class ImmutableByte2CharOpenHashMap extends AbstractByte2CharMap implemen
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1072,7 +1085,7 @@ public class ImmutableByte2CharOpenHashMap extends AbstractByte2CharMap implemen
 		}
 		
 		@Override
-		public char reduce(CharCharUnaryOperator operator) {
+		public OptionalChar reduce(CharCharUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			char state = (char)0;
 			boolean empty = true;
@@ -1087,19 +1100,19 @@ public class ImmutableByte2CharOpenHashMap extends AbstractByte2CharMap implemen
 				state = operator.applyAsChar(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalChar.empty() : OptionalChar.of(state);
 		}
 		
 		@Override
-		public char findFirst(CharPredicate filter) {
+		public OptionalChar findFirst(CharPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (char)0;
+			if(size() <= 0) return OptionalChar.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalChar.of(values[index]);
 				index = (int)links[index];
 			}
-			return (char)0;
+			return OptionalChar.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2DoubleOpenHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.DoublePredicate;
+import java.util.OptionalDouble;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntDoubleConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteDoubleConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2DoubleFunction;
@@ -538,6 +541,10 @@ public class ImmutableByte2DoubleOpenHashMap extends AbstractByte2DoubleMap impl
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2DoubleMap.Entry> implements Byte2DoubleOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -691,7 +698,7 @@ public class ImmutableByte2DoubleOpenHashMap extends AbstractByte2DoubleMap impl
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
+		public Optional<Byte2DoubleMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2DoubleMap.Entry state = null;
 			boolean empty = true;
@@ -706,21 +713,21 @@ public class ImmutableByte2DoubleOpenHashMap extends AbstractByte2DoubleMap impl
 				state = operator.apply(state, new BasicEntry(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
+		public Optional<Byte2DoubleMap.Entry> findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry entry = new BasicEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -783,6 +790,12 @@ public class ImmutableByte2DoubleOpenHashMap extends AbstractByte2DoubleMap impl
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -918,7 +931,7 @@ public class ImmutableByte2DoubleOpenHashMap extends AbstractByte2DoubleMap impl
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -933,19 +946,19 @@ public class ImmutableByte2DoubleOpenHashMap extends AbstractByte2DoubleMap impl
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1072,7 +1085,7 @@ public class ImmutableByte2DoubleOpenHashMap extends AbstractByte2DoubleMap impl
 		}
 		
 		@Override
-		public double reduce(DoubleDoubleUnaryOperator operator) {
+		public OptionalDouble reduce(DoubleDoubleUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			double state = 0D;
 			boolean empty = true;
@@ -1087,19 +1100,19 @@ public class ImmutableByte2DoubleOpenHashMap extends AbstractByte2DoubleMap impl
 				state = operator.applyAsDouble(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalDouble.empty() : OptionalDouble.of(state);
 		}
 		
 		@Override
-		public double findFirst(DoublePredicate filter) {
+		public OptionalDouble findFirst(DoublePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0D;
+			if(size() <= 0) return OptionalDouble.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalDouble.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0D;
+			return OptionalDouble.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2FloatOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntFloatConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteFloatConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2FloatFunction;
@@ -29,6 +31,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectFloatConsumer;
 
 import speiger.src.collections.floats.functions.function.FloatPredicate;
+import speiger.src.collections.floats.functions.OptionalFloat;
 import speiger.src.collections.bytes.sets.AbstractByteSet;
 import speiger.src.collections.floats.collections.AbstractFloatCollection;
 import speiger.src.collections.floats.collections.FloatOrderedCollection;
@@ -538,6 +541,10 @@ public class ImmutableByte2FloatOpenHashMap extends AbstractByte2FloatMap implem
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2FloatMap.Entry> implements Byte2FloatOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -691,7 +698,7 @@ public class ImmutableByte2FloatOpenHashMap extends AbstractByte2FloatMap implem
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
+		public Optional<Byte2FloatMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2FloatMap.Entry state = null;
 			boolean empty = true;
@@ -706,21 +713,21 @@ public class ImmutableByte2FloatOpenHashMap extends AbstractByte2FloatMap implem
 				state = operator.apply(state, new BasicEntry(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry findFirst(Predicate<Byte2FloatMap.Entry> filter) {
+		public Optional<Byte2FloatMap.Entry> findFirst(Predicate<Byte2FloatMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry entry = new BasicEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -783,6 +790,12 @@ public class ImmutableByte2FloatOpenHashMap extends AbstractByte2FloatMap implem
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -918,7 +931,7 @@ public class ImmutableByte2FloatOpenHashMap extends AbstractByte2FloatMap implem
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -933,19 +946,19 @@ public class ImmutableByte2FloatOpenHashMap extends AbstractByte2FloatMap implem
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1072,7 +1085,7 @@ public class ImmutableByte2FloatOpenHashMap extends AbstractByte2FloatMap implem
 		}
 		
 		@Override
-		public float reduce(FloatFloatUnaryOperator operator) {
+		public OptionalFloat reduce(FloatFloatUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			float state = 0F;
 			boolean empty = true;
@@ -1087,19 +1100,19 @@ public class ImmutableByte2FloatOpenHashMap extends AbstractByte2FloatMap implem
 				state = operator.applyAsFloat(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalFloat.empty() : OptionalFloat.of(state);
 		}
 		
 		@Override
-		public float findFirst(FloatPredicate filter) {
+		public OptionalFloat findFirst(FloatPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0F;
+			if(size() <= 0) return OptionalFloat.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalFloat.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0F;
+			return OptionalFloat.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2IntOpenHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.IntPredicate;
+import java.util.OptionalInt;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntIntConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteIntConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2IntFunction;
@@ -538,6 +541,10 @@ public class ImmutableByte2IntOpenHashMap extends AbstractByte2IntMap implements
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2IntMap.Entry> implements Byte2IntOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -691,7 +698,7 @@ public class ImmutableByte2IntOpenHashMap extends AbstractByte2IntMap implements
 		}
 		
 		@Override
-		public Byte2IntMap.Entry reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
+		public Optional<Byte2IntMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2IntMap.Entry state = null;
 			boolean empty = true;
@@ -706,21 +713,21 @@ public class ImmutableByte2IntOpenHashMap extends AbstractByte2IntMap implements
 				state = operator.apply(state, new BasicEntry(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2IntMap.Entry findFirst(Predicate<Byte2IntMap.Entry> filter) {
+		public Optional<Byte2IntMap.Entry> findFirst(Predicate<Byte2IntMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry entry = new BasicEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -783,6 +790,12 @@ public class ImmutableByte2IntOpenHashMap extends AbstractByte2IntMap implements
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -918,7 +931,7 @@ public class ImmutableByte2IntOpenHashMap extends AbstractByte2IntMap implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -933,19 +946,19 @@ public class ImmutableByte2IntOpenHashMap extends AbstractByte2IntMap implements
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1072,7 +1085,7 @@ public class ImmutableByte2IntOpenHashMap extends AbstractByte2IntMap implements
 		}
 		
 		@Override
-		public int reduce(IntIntUnaryOperator operator) {
+		public OptionalInt reduce(IntIntUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			int state = 0;
 			boolean empty = true;
@@ -1087,19 +1100,19 @@ public class ImmutableByte2IntOpenHashMap extends AbstractByte2IntMap implements
 				state = operator.applyAsInt(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalInt.empty() : OptionalInt.of(state);
 		}
 		
 		@Override
-		public int findFirst(IntPredicate filter) {
+		public OptionalInt findFirst(IntPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0;
+			if(size() <= 0) return OptionalInt.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalInt.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0;
+			return OptionalInt.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2LongOpenHashMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.LongPredicate;
+import java.util.OptionalLong;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntLongConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteLongConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2LongFunction;
@@ -538,6 +541,10 @@ public class ImmutableByte2LongOpenHashMap extends AbstractByte2LongMap implemen
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2LongMap.Entry> implements Byte2LongOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -691,7 +698,7 @@ public class ImmutableByte2LongOpenHashMap extends AbstractByte2LongMap implemen
 		}
 		
 		@Override
-		public Byte2LongMap.Entry reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
+		public Optional<Byte2LongMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2LongMap.Entry state = null;
 			boolean empty = true;
@@ -706,21 +713,21 @@ public class ImmutableByte2LongOpenHashMap extends AbstractByte2LongMap implemen
 				state = operator.apply(state, new BasicEntry(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2LongMap.Entry findFirst(Predicate<Byte2LongMap.Entry> filter) {
+		public Optional<Byte2LongMap.Entry> findFirst(Predicate<Byte2LongMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry entry = new BasicEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -783,6 +790,12 @@ public class ImmutableByte2LongOpenHashMap extends AbstractByte2LongMap implemen
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -918,7 +931,7 @@ public class ImmutableByte2LongOpenHashMap extends AbstractByte2LongMap implemen
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -933,19 +946,19 @@ public class ImmutableByte2LongOpenHashMap extends AbstractByte2LongMap implemen
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1072,7 +1085,7 @@ public class ImmutableByte2LongOpenHashMap extends AbstractByte2LongMap implemen
 		}
 		
 		@Override
-		public long reduce(LongLongUnaryOperator operator) {
+		public OptionalLong reduce(LongLongUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			long state = 0L;
 			boolean empty = true;
@@ -1087,19 +1100,19 @@ public class ImmutableByte2LongOpenHashMap extends AbstractByte2LongMap implemen
 				state = operator.applyAsLong(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalLong.empty() : OptionalLong.of(state);
 		}
 		
 		@Override
-		public long findFirst(LongPredicate filter) {
+		public OptionalLong findFirst(LongPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return 0L;
+			if(size() <= 0) return OptionalLong.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalLong.of(values[index]);
 				index = (int)links[index];
 			}
-			return 0L;
+			return OptionalLong.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2ObjectOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -13,6 +14,7 @@ import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteObjectConsumer;
 import speiger.src.collections.bytes.functions.function.ByteFunction;
@@ -509,6 +511,10 @@ public class ImmutableByte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ObjectMap.Entry<V>> implements Byte2ObjectOrderedMap.FastOrderedSet<V> {
+		@Override
+		public void addFirst(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -662,7 +668,7 @@ public class ImmutableByte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
+		public Optional<Byte2ObjectMap.Entry<V>> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ObjectMap.Entry<V> state = null;
 			boolean empty = true;
@@ -677,21 +683,21 @@ public class ImmutableByte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V
 				state = operator.apply(state, new BasicEntry<>(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
+		public Optional<Byte2ObjectMap.Entry<V>> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry<V> entry = new BasicEntry<>();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -754,6 +760,12 @@ public class ImmutableByte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -889,7 +901,7 @@ public class ImmutableByte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -904,19 +916,19 @@ public class ImmutableByte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1044,7 +1056,7 @@ public class ImmutableByte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V
 		}
 		
 		@Override
-		public V reduce(ObjectObjectUnaryOperator<V, V> operator) {
+		public Optional<V> reduce(ObjectObjectUnaryOperator<V, V> operator) {
 			Objects.requireNonNull(operator);
 			V state = null;
 			boolean empty = true;
@@ -1059,19 +1071,19 @@ public class ImmutableByte2ObjectOpenHashMap<V> extends AbstractByte2ObjectMap<V
 				state = operator.apply(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public V findFirst(Predicate<V> filter) {
+		public Optional<V> findFirst(Predicate<V> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return Optional.ofNullable(values[index]);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/immutable/ImmutableByte2ShortOpenHashMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntShortConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteShortConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2ShortFunction;
@@ -29,6 +31,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectShortConsumer;
 
 import speiger.src.collections.shorts.functions.function.ShortPredicate;
+import speiger.src.collections.shorts.functions.OptionalShort;
 import speiger.src.collections.bytes.sets.AbstractByteSet;
 import speiger.src.collections.shorts.collections.AbstractShortCollection;
 import speiger.src.collections.shorts.collections.ShortOrderedCollection;
@@ -538,6 +541,10 @@ public class ImmutableByte2ShortOpenHashMap extends AbstractByte2ShortMap implem
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ShortMap.Entry> implements Byte2ShortOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -691,7 +698,7 @@ public class ImmutableByte2ShortOpenHashMap extends AbstractByte2ShortMap implem
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
+		public Optional<Byte2ShortMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ShortMap.Entry state = null;
 			boolean empty = true;
@@ -706,21 +713,21 @@ public class ImmutableByte2ShortOpenHashMap extends AbstractByte2ShortMap implem
 				state = operator.apply(state, new BasicEntry(keys[index], values[index]));
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry findFirst(Predicate<Byte2ShortMap.Entry> filter) {
+		public Optional<Byte2ShortMap.Entry> findFirst(Predicate<Byte2ShortMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry entry = new BasicEntry();
 			int index = firstIndex;
 			while(index != -1) {
 				entry.set(keys[index], values[index]);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 				index = (int)links[index];
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -783,6 +790,12 @@ public class ImmutableByte2ShortOpenHashMap extends AbstractByte2ShortMap implem
 			throw new UnsupportedOperationException();
 		}
 		
+		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		
 		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 
@@ -918,7 +931,7 @@ public class ImmutableByte2ShortOpenHashMap extends AbstractByte2ShortMap implem
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -933,19 +946,19 @@ public class ImmutableByte2ShortOpenHashMap extends AbstractByte2ShortMap implem
 				state = operator.applyAsByte(state, keys[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (byte)0;
+			if(size() <= 0) return OptionalByte.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(keys[index])) return keys[index];
+				if(filter.test(keys[index])) return OptionalByte.of(keys[index]);
 				index = (int)links[index];
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1072,7 +1085,7 @@ public class ImmutableByte2ShortOpenHashMap extends AbstractByte2ShortMap implem
 		}
 		
 		@Override
-		public short reduce(ShortShortUnaryOperator operator) {
+		public OptionalShort reduce(ShortShortUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			short state = (short)0;
 			boolean empty = true;
@@ -1087,19 +1100,19 @@ public class ImmutableByte2ShortOpenHashMap extends AbstractByte2ShortMap implem
 				state = operator.applyAsShort(state, values[index]);
 				index = (int)links[index];
 			}
-			return state;
+			return empty ? OptionalShort.empty() : OptionalShort.of(state);
 		}
 		
 		@Override
-		public short findFirst(ShortPredicate filter) {
+		public OptionalShort findFirst(ShortPredicate filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return (short)0;
+			if(size() <= 0) return OptionalShort.empty();
 			int index = firstIndex;
 			while(index != -1){
-				if(filter.test(values[index])) return values[index];
+				if(filter.test(values[index])) return OptionalShort.of(values[index]);
 				index = (int)links[index];
 			}
-			return (short)0;
+			return OptionalShort.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2BooleanArrayMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.function.ByteBooleanUnaryOperator;
@@ -34,6 +36,7 @@ import speiger.src.collections.booleans.lists.BooleanListIterator;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
@@ -728,6 +731,10 @@ public class Byte2BooleanArrayMap extends AbstractByte2BooleanMap implements Byt
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2BooleanMap.Entry> implements Byte2BooleanOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2BooleanMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -876,7 +883,7 @@ public class Byte2BooleanArrayMap extends AbstractByte2BooleanMap implements Byt
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -888,19 +895,19 @@ public class Byte2BooleanArrayMap extends AbstractByte2BooleanMap implements Byt
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -973,6 +980,10 @@ public class Byte2BooleanArrayMap extends AbstractByte2BooleanMap implements Byt
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -1059,7 +1070,7 @@ public class Byte2BooleanArrayMap extends AbstractByte2BooleanMap implements Byt
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1071,16 +1082,16 @@ public class Byte2BooleanArrayMap extends AbstractByte2BooleanMap implements Byt
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1181,7 +1192,7 @@ public class Byte2BooleanArrayMap extends AbstractByte2BooleanMap implements Byt
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -1193,16 +1204,16 @@ public class Byte2BooleanArrayMap extends AbstractByte2BooleanMap implements Byt
 				}
 				state = operator.applyAsBoolean(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return OptionalBoolean.of(values[i]);
 			}
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2ByteArrayMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -13,6 +14,7 @@ import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteByteConsumer;
 import speiger.src.collections.bytes.functions.function.ByteUnaryOperator;
@@ -744,6 +746,10 @@ public class Byte2ByteArrayMap extends AbstractByte2ByteMap implements Byte2Byte
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ByteMap.Entry> implements Byte2ByteOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ByteMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -892,7 +898,7 @@ public class Byte2ByteArrayMap extends AbstractByte2ByteMap implements Byte2Byte
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
+		public Optional<Byte2ByteMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ByteMap.Entry, Byte2ByteMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ByteMap.Entry state = null;
 			boolean empty = true;
@@ -904,19 +910,19 @@ public class Byte2ByteArrayMap extends AbstractByte2ByteMap implements Byte2Byte
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ByteMap.Entry findFirst(Predicate<Byte2ByteMap.Entry> filter) {
+		public Optional<Byte2ByteMap.Entry> findFirst(Predicate<Byte2ByteMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -989,6 +995,10 @@ public class Byte2ByteArrayMap extends AbstractByte2ByteMap implements Byte2Byte
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -1075,7 +1085,7 @@ public class Byte2ByteArrayMap extends AbstractByte2ByteMap implements Byte2Byte
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1087,16 +1097,16 @@ public class Byte2ByteArrayMap extends AbstractByte2ByteMap implements Byte2Byte
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1197,7 +1207,7 @@ public class Byte2ByteArrayMap extends AbstractByte2ByteMap implements Byte2Byte
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1209,16 +1219,16 @@ public class Byte2ByteArrayMap extends AbstractByte2ByteMap implements Byte2Byte
 				}
 				state = operator.applyAsByte(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return OptionalByte.of(values[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2CharArrayMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntCharConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteCharConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2CharFunction;
@@ -35,6 +37,7 @@ import speiger.src.collections.chars.lists.CharListIterator;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 
 import speiger.src.collections.chars.functions.function.CharPredicate;
+import speiger.src.collections.chars.functions.OptionalChar;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
@@ -751,6 +754,10 @@ public class Byte2CharArrayMap extends AbstractByte2CharMap implements Byte2Char
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2CharMap.Entry> implements Byte2CharOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2CharMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -899,7 +906,7 @@ public class Byte2CharArrayMap extends AbstractByte2CharMap implements Byte2Char
 		}
 		
 		@Override
-		public Byte2CharMap.Entry reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
+		public Optional<Byte2CharMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2CharMap.Entry, Byte2CharMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2CharMap.Entry state = null;
 			boolean empty = true;
@@ -911,19 +918,19 @@ public class Byte2CharArrayMap extends AbstractByte2CharMap implements Byte2Char
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2CharMap.Entry findFirst(Predicate<Byte2CharMap.Entry> filter) {
+		public Optional<Byte2CharMap.Entry> findFirst(Predicate<Byte2CharMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -996,6 +1003,10 @@ public class Byte2CharArrayMap extends AbstractByte2CharMap implements Byte2Char
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -1082,7 +1093,7 @@ public class Byte2CharArrayMap extends AbstractByte2CharMap implements Byte2Char
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1094,16 +1105,16 @@ public class Byte2CharArrayMap extends AbstractByte2CharMap implements Byte2Char
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1204,7 +1215,7 @@ public class Byte2CharArrayMap extends AbstractByte2CharMap implements Byte2Char
 		}
 		
 		@Override
-		public char reduce(CharCharUnaryOperator operator) {
+		public OptionalChar reduce(CharCharUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			char state = (char)0;
 			boolean empty = true;
@@ -1216,16 +1227,16 @@ public class Byte2CharArrayMap extends AbstractByte2CharMap implements Byte2Char
 				}
 				state = operator.applyAsChar(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalChar.empty() : OptionalChar.of(state);
 		}
 		
 		@Override
-		public char findFirst(CharPredicate filter) {
+		public OptionalChar findFirst(CharPredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return OptionalChar.of(values[i]);
 			}
-			return (char)0;
+			return OptionalChar.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2DoubleArrayMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.DoublePredicate;
+import java.util.OptionalDouble;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntDoubleConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteDoubleConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2DoubleFunction;
@@ -751,6 +754,10 @@ public class Byte2DoubleArrayMap extends AbstractByte2DoubleMap implements Byte2
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2DoubleMap.Entry> implements Byte2DoubleOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2DoubleMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -899,7 +906,7 @@ public class Byte2DoubleArrayMap extends AbstractByte2DoubleMap implements Byte2
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
+		public Optional<Byte2DoubleMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2DoubleMap.Entry, Byte2DoubleMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2DoubleMap.Entry state = null;
 			boolean empty = true;
@@ -911,19 +918,19 @@ public class Byte2DoubleArrayMap extends AbstractByte2DoubleMap implements Byte2
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2DoubleMap.Entry findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
+		public Optional<Byte2DoubleMap.Entry> findFirst(Predicate<Byte2DoubleMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -996,6 +1003,10 @@ public class Byte2DoubleArrayMap extends AbstractByte2DoubleMap implements Byte2
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -1082,7 +1093,7 @@ public class Byte2DoubleArrayMap extends AbstractByte2DoubleMap implements Byte2
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1094,16 +1105,16 @@ public class Byte2DoubleArrayMap extends AbstractByte2DoubleMap implements Byte2
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1204,7 +1215,7 @@ public class Byte2DoubleArrayMap extends AbstractByte2DoubleMap implements Byte2
 		}
 		
 		@Override
-		public double reduce(DoubleDoubleUnaryOperator operator) {
+		public OptionalDouble reduce(DoubleDoubleUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			double state = 0D;
 			boolean empty = true;
@@ -1216,16 +1227,16 @@ public class Byte2DoubleArrayMap extends AbstractByte2DoubleMap implements Byte2
 				}
 				state = operator.applyAsDouble(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalDouble.empty() : OptionalDouble.of(state);
 		}
 		
 		@Override
-		public double findFirst(DoublePredicate filter) {
+		public OptionalDouble findFirst(DoublePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return OptionalDouble.of(values[i]);
 			}
-			return 0D;
+			return OptionalDouble.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2FloatArrayMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntFloatConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteFloatConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2FloatFunction;
@@ -35,6 +37,7 @@ import speiger.src.collections.floats.lists.FloatListIterator;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 
 import speiger.src.collections.floats.functions.function.FloatPredicate;
+import speiger.src.collections.floats.functions.OptionalFloat;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
@@ -751,6 +754,10 @@ public class Byte2FloatArrayMap extends AbstractByte2FloatMap implements Byte2Fl
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2FloatMap.Entry> implements Byte2FloatOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2FloatMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -899,7 +906,7 @@ public class Byte2FloatArrayMap extends AbstractByte2FloatMap implements Byte2Fl
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
+		public Optional<Byte2FloatMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2FloatMap.Entry, Byte2FloatMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2FloatMap.Entry state = null;
 			boolean empty = true;
@@ -911,19 +918,19 @@ public class Byte2FloatArrayMap extends AbstractByte2FloatMap implements Byte2Fl
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2FloatMap.Entry findFirst(Predicate<Byte2FloatMap.Entry> filter) {
+		public Optional<Byte2FloatMap.Entry> findFirst(Predicate<Byte2FloatMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -996,6 +1003,10 @@ public class Byte2FloatArrayMap extends AbstractByte2FloatMap implements Byte2Fl
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -1082,7 +1093,7 @@ public class Byte2FloatArrayMap extends AbstractByte2FloatMap implements Byte2Fl
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1094,16 +1105,16 @@ public class Byte2FloatArrayMap extends AbstractByte2FloatMap implements Byte2Fl
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1204,7 +1215,7 @@ public class Byte2FloatArrayMap extends AbstractByte2FloatMap implements Byte2Fl
 		}
 		
 		@Override
-		public float reduce(FloatFloatUnaryOperator operator) {
+		public OptionalFloat reduce(FloatFloatUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			float state = 0F;
 			boolean empty = true;
@@ -1216,16 +1227,16 @@ public class Byte2FloatArrayMap extends AbstractByte2FloatMap implements Byte2Fl
 				}
 				state = operator.applyAsFloat(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalFloat.empty() : OptionalFloat.of(state);
 		}
 		
 		@Override
-		public float findFirst(FloatPredicate filter) {
+		public OptionalFloat findFirst(FloatPredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return OptionalFloat.of(values[i]);
 			}
-			return 0F;
+			return OptionalFloat.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2IntArrayMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.IntPredicate;
+import java.util.OptionalInt;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntIntConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteIntConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2IntFunction;
@@ -751,6 +754,10 @@ public class Byte2IntArrayMap extends AbstractByte2IntMap implements Byte2IntOrd
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2IntMap.Entry> implements Byte2IntOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2IntMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -899,7 +906,7 @@ public class Byte2IntArrayMap extends AbstractByte2IntMap implements Byte2IntOrd
 		}
 		
 		@Override
-		public Byte2IntMap.Entry reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
+		public Optional<Byte2IntMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2IntMap.Entry, Byte2IntMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2IntMap.Entry state = null;
 			boolean empty = true;
@@ -911,19 +918,19 @@ public class Byte2IntArrayMap extends AbstractByte2IntMap implements Byte2IntOrd
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2IntMap.Entry findFirst(Predicate<Byte2IntMap.Entry> filter) {
+		public Optional<Byte2IntMap.Entry> findFirst(Predicate<Byte2IntMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -996,6 +1003,10 @@ public class Byte2IntArrayMap extends AbstractByte2IntMap implements Byte2IntOrd
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -1082,7 +1093,7 @@ public class Byte2IntArrayMap extends AbstractByte2IntMap implements Byte2IntOrd
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1094,16 +1105,16 @@ public class Byte2IntArrayMap extends AbstractByte2IntMap implements Byte2IntOrd
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1204,7 +1215,7 @@ public class Byte2IntArrayMap extends AbstractByte2IntMap implements Byte2IntOrd
 		}
 		
 		@Override
-		public int reduce(IntIntUnaryOperator operator) {
+		public OptionalInt reduce(IntIntUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			int state = 0;
 			boolean empty = true;
@@ -1216,16 +1227,16 @@ public class Byte2IntArrayMap extends AbstractByte2IntMap implements Byte2IntOrd
 				}
 				state = operator.applyAsInt(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalInt.empty() : OptionalInt.of(state);
 		}
 		
 		@Override
-		public int findFirst(IntPredicate filter) {
+		public OptionalInt findFirst(IntPredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return OptionalInt.of(values[i]);
 			}
-			return 0;
+			return OptionalInt.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2LongArrayMap.java

@@ -4,10 +4,12 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
 import java.util.function.LongPredicate;
+import java.util.OptionalLong;
 
 import speiger.src.collections.bytes.collections.ByteBidirectionalIterator;
 import speiger.src.collections.bytes.functions.ByteConsumer;
@@ -15,6 +17,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntLongConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteLongConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2LongFunction;
@@ -751,6 +754,10 @@ public class Byte2LongArrayMap extends AbstractByte2LongMap implements Byte2Long
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2LongMap.Entry> implements Byte2LongOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2LongMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -899,7 +906,7 @@ public class Byte2LongArrayMap extends AbstractByte2LongMap implements Byte2Long
 		}
 		
 		@Override
-		public Byte2LongMap.Entry reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
+		public Optional<Byte2LongMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2LongMap.Entry, Byte2LongMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2LongMap.Entry state = null;
 			boolean empty = true;
@@ -911,19 +918,19 @@ public class Byte2LongArrayMap extends AbstractByte2LongMap implements Byte2Long
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2LongMap.Entry findFirst(Predicate<Byte2LongMap.Entry> filter) {
+		public Optional<Byte2LongMap.Entry> findFirst(Predicate<Byte2LongMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -996,6 +1003,10 @@ public class Byte2LongArrayMap extends AbstractByte2LongMap implements Byte2Long
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -1082,7 +1093,7 @@ public class Byte2LongArrayMap extends AbstractByte2LongMap implements Byte2Long
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1094,16 +1105,16 @@ public class Byte2LongArrayMap extends AbstractByte2LongMap implements Byte2Long
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1204,7 +1215,7 @@ public class Byte2LongArrayMap extends AbstractByte2LongMap implements Byte2Long
 		}
 		
 		@Override
-		public long reduce(LongLongUnaryOperator operator) {
+		public OptionalLong reduce(LongLongUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			long state = 0L;
 			boolean empty = true;
@@ -1216,16 +1227,16 @@ public class Byte2LongArrayMap extends AbstractByte2LongMap implements Byte2Long
 				}
 				state = operator.applyAsLong(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalLong.empty() : OptionalLong.of(state);
 		}
 		
 		@Override
-		public long findFirst(LongPredicate filter) {
+		public OptionalLong findFirst(LongPredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return OptionalLong.of(values[i]);
 			}
-			return 0L;
+			return OptionalLong.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2ObjectArrayMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -13,6 +14,7 @@ import speiger.src.collections.bytes.functions.ByteConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteObjectConsumer;
 import speiger.src.collections.bytes.functions.function.ByteFunction;
@@ -664,6 +666,10 @@ public class Byte2ObjectArrayMap<V> extends AbstractByte2ObjectMap<V> implements
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ObjectMap.Entry<V>> implements Byte2ObjectOrderedMap.FastOrderedSet<V> {
+		@Override
+		public void addFirst(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ObjectMap.Entry<V> o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -812,7 +818,7 @@ public class Byte2ObjectArrayMap<V> extends AbstractByte2ObjectMap<V> implements
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
+		public Optional<Byte2ObjectMap.Entry<V>> reduce(ObjectObjectUnaryOperator<Byte2ObjectMap.Entry<V>, Byte2ObjectMap.Entry<V>> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ObjectMap.Entry<V> state = null;
 			boolean empty = true;
@@ -824,19 +830,19 @@ public class Byte2ObjectArrayMap<V> extends AbstractByte2ObjectMap<V> implements
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ObjectMap.Entry<V> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
+		public Optional<Byte2ObjectMap.Entry<V>> findFirst(Predicate<Byte2ObjectMap.Entry<V>> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -909,6 +915,10 @@ public class Byte2ObjectArrayMap<V> extends AbstractByte2ObjectMap<V> implements
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -995,7 +1005,7 @@ public class Byte2ObjectArrayMap<V> extends AbstractByte2ObjectMap<V> implements
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1007,16 +1017,16 @@ public class Byte2ObjectArrayMap<V> extends AbstractByte2ObjectMap<V> implements
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1117,7 +1127,7 @@ public class Byte2ObjectArrayMap<V> extends AbstractByte2ObjectMap<V> implements
 		}
 		
 		@Override
-		public V reduce(ObjectObjectUnaryOperator<V, V> operator) {
+		public Optional<V> reduce(ObjectObjectUnaryOperator<V, V> operator) {
 			Objects.requireNonNull(operator);
 			V state = null;
 			boolean empty = true;
@@ -1129,16 +1139,16 @@ public class Byte2ObjectArrayMap<V> extends AbstractByte2ObjectMap<V> implements
 				}
 				state = operator.apply(state, values[i]);
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public V findFirst(Predicate<V> filter) {
+		public Optional<V> findFirst(Predicate<V> filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return Optional.ofNullable(values[i]);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/misc/Byte2ShortArrayMap.java

@@ -4,6 +4,7 @@ import java.util.Arrays;
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
 import java.util.function.Predicate;
@@ -14,6 +15,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntByteConsumer;
 import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntShortConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteShortConsumer;
 import speiger.src.collections.bytes.functions.function.Byte2ShortFunction;
@@ -35,6 +37,7 @@ import speiger.src.collections.shorts.lists.ShortListIterator;
 import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 
 import speiger.src.collections.shorts.functions.function.ShortPredicate;
+import speiger.src.collections.shorts.functions.OptionalShort;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
@@ -751,6 +754,10 @@ public class Byte2ShortArrayMap extends AbstractByte2ShortMap implements Byte2Sh
 	}
 	
 	private class MapEntrySet extends AbstractObjectSet<Byte2ShortMap.Entry> implements Byte2ShortOrderedMap.FastOrderedSet {
+		@Override
+		public void addFirst(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToFirst(Byte2ShortMap.Entry o) { throw new UnsupportedOperationException(); }
 		@Override
@@ -899,7 +906,7 @@ public class Byte2ShortArrayMap extends AbstractByte2ShortMap implements Byte2Sh
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
+		public Optional<Byte2ShortMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2ShortMap.Entry, Byte2ShortMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2ShortMap.Entry state = null;
 			boolean empty = true;
@@ -911,19 +918,19 @@ public class Byte2ShortArrayMap extends AbstractByte2ShortMap implements Byte2Sh
 				}
 				state = operator.apply(state, new ValueMapEntry(i));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2ShortMap.Entry findFirst(Predicate<Byte2ShortMap.Entry> filter) {
+		public Optional<Byte2ShortMap.Entry> findFirst(Predicate<Byte2ShortMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			MapEntry entry = new MapEntry();
 			for(int i = 0;i<size;i++) {
 				entry.set(i);
-				if(filter.test(entry)) return entry;
+				if(filter.test(entry)) return Optional.ofNullable(entry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override
@@ -996,6 +1003,10 @@ public class Byte2ShortArrayMap extends AbstractByte2ShortMap implements Byte2Sh
 		@Override
 		public boolean add(byte o) { throw new UnsupportedOperationException(); }
 		@Override
+		public void addFirst(byte o) { throw new UnsupportedOperationException(); }
+		@Override
+		public void addLast(byte o) { throw new UnsupportedOperationException(); }
+		@Override
 		public boolean addAndMoveToFirst(byte o) { throw new UnsupportedOperationException(); }
 		@Override
 		public boolean addAndMoveToLast(byte o) { throw new UnsupportedOperationException(); }
@@ -1082,7 +1093,7 @@ public class Byte2ShortArrayMap extends AbstractByte2ShortMap implements Byte2Sh
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1094,16 +1105,16 @@ public class Byte2ShortArrayMap extends AbstractByte2ShortMap implements Byte2Sh
 				}
 				state = operator.applyAsByte(state, keys[i]);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(keys[i])) return keys[i];
+				if(filter.test(keys[i])) return OptionalByte.of(keys[i]);
 			}
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1204,7 +1215,7 @@ public class Byte2ShortArrayMap extends AbstractByte2ShortMap implements Byte2Sh
 		}
 		
 		@Override
-		public short reduce(ShortShortUnaryOperator operator) {
+		public OptionalShort reduce(ShortShortUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			short state = (short)0;
 			boolean empty = true;
@@ -1216,16 +1227,16 @@ public class Byte2ShortArrayMap extends AbstractByte2ShortMap implements Byte2Sh
 				}
 				state = operator.applyAsShort(state, values[i]);
 			}
-			return state;
+			return empty ? OptionalShort.empty() : OptionalShort.of(state);
 		}
 		
 		@Override
-		public short findFirst(ShortPredicate filter) {
+		public OptionalShort findFirst(ShortPredicate filter) {
 			Objects.requireNonNull(filter);
 			for(int i = 0;i<size;i++) {
-				if(filter.test(values[i])) return values[i];
+				if(filter.test(values[i])) return OptionalShort.of(values[i]);
 			}
-			return (short)0;
+			return OptionalShort.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/tree/Byte2BooleanAVLTreeMap.java

@@ -3,6 +3,7 @@ package speiger.src.collections.bytes.maps.impl.tree;
 import java.util.Collections;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.NoSuchElementException;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
@@ -18,6 +19,7 @@ import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.ByteBooleanUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2BooleanMap;
@@ -36,6 +38,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
@@ -1070,7 +1073,7 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1082,15 +1085,15 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 				}
 				state = operator.applyAsByte(state, entry.key);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(Node entry = start(), end = end();entry != null && (end == null || (end != previous(entry)));entry = next(entry))
-				if(filter.test(entry.key)) return entry.key;
+				if(filter.test(entry.key)) return OptionalByte.of(entry.key);
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1712,7 +1715,7 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 			}
 			
 			@Override
-			public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+			public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 				Objects.requireNonNull(operator);
 				Byte2BooleanMap.Entry state = null;
 				boolean empty = true;
@@ -1724,19 +1727,19 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 					}
 					state = operator.apply(state, new BasicEntry(entry.key, entry.value));
 				}
-				return state;
+				return empty ? Optional.empty() : Optional.ofNullable(state);
 			}
 			
 			@Override
-			public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+			public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 				Objects.requireNonNull(filter);
-				if(size() <= 0) return null;
+				if(size() <= 0) return Optional.empty();
 				BasicEntry subEntry = new BasicEntry();
 				for(Node entry = subLowest(), last = subHighest();entry != null && (last == null || last != previous(entry));entry = next(entry)) {
 					subEntry.set(entry.key, entry.value);
-					if(filter.test(subEntry)) return subEntry;
+					if(filter.test(subEntry)) return Optional.ofNullable(subEntry);
 				}
-				return null;
+				return Optional.empty();
 			}
 			
 			@Override
@@ -1831,7 +1834,7 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 			}
 			
 			@Override
-			public boolean reduce(BooleanBooleanUnaryOperator operator) {
+			public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 				Objects.requireNonNull(operator);
 				boolean state = false;
 				boolean empty = true;
@@ -1843,15 +1846,15 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 					}
 					state = operator.applyAsBoolean(state, entry.value);
 				}
-				return state;
+				return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 			}
 			
 			@Override
-			public boolean findFirst(BooleanPredicate filter) {
+			public OptionalBoolean findFirst(BooleanPredicate filter) {
 				Objects.requireNonNull(filter);
 				for(Node entry = subLowest(), last = subHighest();entry != null && (last == null || last != previous(entry));entry = next(entry))
-					if(filter.test(entry.value)) return entry.value;
+					if(filter.test(entry.value)) return OptionalBoolean.of(entry.value);
-				return false;
+				return OptionalBoolean.empty();
 			}
 			
 			@Override
@@ -2167,7 +2170,7 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -2179,15 +2182,15 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 				}
 				state = operator.applyAsBoolean(state, entry.value);
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
 			for(Node entry = first;entry != null;entry = entry.next())
-				if(filter.test(entry.value)) return entry.value;
+				if(filter.test(entry.value)) return OptionalBoolean.of(entry.value);
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override
@@ -2328,7 +2331,7 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -2340,19 +2343,19 @@ public class Byte2BooleanAVLTreeMap extends AbstractByte2BooleanMap implements B
 				}
 				state = operator.apply(state, new BasicEntry(entry.key, entry.value));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry subEntry = new BasicEntry();
 			for(Node entry = first;entry != null;entry = entry.next()) {
 				subEntry.set(entry.key, entry.value);
-				if(filter.test(subEntry)) return subEntry;
+				if(filter.test(subEntry)) return Optional.ofNullable(subEntry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override

src/main/java/speiger/src/collections/bytes/maps/impl/tree/Byte2BooleanRBTreeMap.java

@@ -3,6 +3,7 @@ package speiger.src.collections.bytes.maps.impl.tree;
 import java.util.Collections;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.NoSuchElementException;
 import java.util.function.Consumer;
 import java.util.function.BiFunction;
@@ -17,6 +18,7 @@ import speiger.src.collections.ints.functions.consumer.IntObjectConsumer;
 import speiger.src.collections.ints.functions.consumer.IntBooleanConsumer;
 import speiger.src.collections.bytes.functions.function.BytePredicate;
 import speiger.src.collections.bytes.functions.consumer.ByteBooleanConsumer;
+import speiger.src.collections.bytes.functions.OptionalByte;
 import speiger.src.collections.bytes.functions.function.ByteBooleanUnaryOperator;
 import speiger.src.collections.bytes.functions.function.ByteByteUnaryOperator;
 import speiger.src.collections.bytes.maps.abstracts.AbstractByte2BooleanMap;
@@ -35,6 +37,7 @@ import speiger.src.collections.objects.functions.consumer.ObjectObjectConsumer;
 import speiger.src.collections.objects.functions.consumer.ObjectBooleanConsumer;
 
 import speiger.src.collections.booleans.functions.function.BooleanPredicate;
+import speiger.src.collections.booleans.functions.OptionalBoolean;
 import speiger.src.collections.objects.collections.ObjectBidirectionalIterator;
 import speiger.src.collections.objects.collections.ObjectIterator;
 import speiger.src.collections.objects.functions.function.ObjectObjectUnaryOperator;
@@ -1123,7 +1126,7 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 		}
 		
 		@Override
-		public byte reduce(ByteByteUnaryOperator operator) {
+		public OptionalByte reduce(ByteByteUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			byte state = (byte)0;
 			boolean empty = true;
@@ -1135,15 +1138,15 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 				}
 				state = operator.applyAsByte(state, entry.key);
 			}
-			return state;
+			return empty ? OptionalByte.empty() : OptionalByte.of(state);
 		}
 		
 		@Override
-		public byte findFirst(BytePredicate filter) {
+		public OptionalByte findFirst(BytePredicate filter) {
 			Objects.requireNonNull(filter);
 			for(Node entry = start(), end = end();entry != null && (end == null || (end != previous(entry)));entry = next(entry))
-				if(filter.test(entry.key)) return entry.key;
+				if(filter.test(entry.key)) return OptionalByte.of(entry.key);
-			return (byte)0;
+			return OptionalByte.empty();
 		}
 		
 		@Override
@@ -1775,7 +1778,7 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 			}
 			
 			@Override
-			public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+			public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 				Objects.requireNonNull(operator);
 				Byte2BooleanMap.Entry state = null;
 				boolean empty = true;
@@ -1787,19 +1790,19 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 					}
 					state = operator.apply(state, new BasicEntry(entry.key, entry.value));
 				}
-				return state;
+				return empty ? Optional.empty() : Optional.ofNullable(state);
 			}
 			
 			@Override
-			public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+			public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 				Objects.requireNonNull(filter);
-				if(size() <= 0) return null;
+				if(size() <= 0) return Optional.empty();
 				BasicEntry subEntry = new BasicEntry();
 				for(Node entry = subLowest(), last = subHighest();entry != null && (last == null || last != previous(entry));entry = next(entry)) {
 					subEntry.set(entry.key, entry.value);
-					if(filter.test(subEntry)) return subEntry;
+					if(filter.test(subEntry)) return Optional.ofNullable(subEntry);
 				}
-				return null;
+				return Optional.empty();
 			}
 			
 			@Override
@@ -1894,7 +1897,7 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 			}
 			
 			@Override
-			public boolean reduce(BooleanBooleanUnaryOperator operator) {
+			public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 				Objects.requireNonNull(operator);
 				boolean state = false;
 				boolean empty = true;
@@ -1906,15 +1909,15 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 					}
 					state = operator.applyAsBoolean(state, entry.value);
 				}
-				return state;
+				return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 			}
 			
 			@Override
-			public boolean findFirst(BooleanPredicate filter) {
+			public OptionalBoolean findFirst(BooleanPredicate filter) {
 				Objects.requireNonNull(filter);
 				for(Node entry = subLowest(), last = subHighest();entry != null && (last == null || last != previous(entry));entry = next(entry))
-					if(filter.test(entry.value)) return entry.value;
+					if(filter.test(entry.value)) return OptionalBoolean.of(entry.value);
-				return false;
+				return OptionalBoolean.empty();
 			}
 			
 			@Override
@@ -2230,7 +2233,7 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 		}
 		
 		@Override
-		public boolean reduce(BooleanBooleanUnaryOperator operator) {
+		public OptionalBoolean reduce(BooleanBooleanUnaryOperator operator) {
 			Objects.requireNonNull(operator);
 			boolean state = false;
 			boolean empty = true;
@@ -2242,15 +2245,15 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 				}
 				state = operator.applyAsBoolean(state, entry.value);
 			}
-			return state;
+			return empty ? OptionalBoolean.empty() : OptionalBoolean.of(state);
 		}
 		
 		@Override
-		public boolean findFirst(BooleanPredicate filter) {
+		public OptionalBoolean findFirst(BooleanPredicate filter) {
 			Objects.requireNonNull(filter);
 			for(Node entry = first;entry != null;entry = entry.next())
-				if(filter.test(entry.value)) return entry.value;
+				if(filter.test(entry.value)) return OptionalBoolean.of(entry.value);
-			return false;
+			return OptionalBoolean.empty();
 		}
 		
 		@Override
@@ -2391,7 +2394,7 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
+		public Optional<Byte2BooleanMap.Entry> reduce(ObjectObjectUnaryOperator<Byte2BooleanMap.Entry, Byte2BooleanMap.Entry> operator) {
 			Objects.requireNonNull(operator);
 			Byte2BooleanMap.Entry state = null;
 			boolean empty = true;
@@ -2403,19 +2406,19 @@ public class Byte2BooleanRBTreeMap extends AbstractByte2BooleanMap implements By
 				}
 				state = operator.apply(state, new BasicEntry(entry.key, entry.value));
 			}
-			return state;
+			return empty ? Optional.empty() : Optional.ofNullable(state);
 		}
 		
 		@Override
-		public Byte2BooleanMap.Entry findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
+		public Optional<Byte2BooleanMap.Entry> findFirst(Predicate<Byte2BooleanMap.Entry> filter) {
 			Objects.requireNonNull(filter);
-			if(size() <= 0) return null;
+			if(size() <= 0) return Optional.empty();
 			BasicEntry subEntry = new BasicEntry();
 			for(Node entry = first;entry != null;entry = entry.next()) {
 				subEntry.set(entry.key, entry.value);
-				if(filter.test(subEntry)) return subEntry;
+				if(filter.test(subEntry)) return Optional.ofNullable(subEntry);
 			}
-			return null;
+			return Optional.empty();
 		}
 		
 		@Override