Make dynamic maps return empty immutable collections instead of throwing

common/src/main/java/org/embeddedt/modernfix/util/DynamicInt2ObjectMap.java

@@ -2,8 +2,11 @@ package org.embeddedt.modernfix.util;
 
 import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
 import it.unimi.dsi.fastutil.ints.IntSet;
+import it.unimi.dsi.fastutil.ints.IntSets;
 import it.unimi.dsi.fastutil.objects.ObjectCollection;
+import it.unimi.dsi.fastutil.objects.ObjectLists;
 import it.unimi.dsi.fastutil.objects.ObjectSet;
+import it.unimi.dsi.fastutil.objects.ObjectSets;
 
 import java.util.Map;
 import java.util.function.Function;
@@ -15,17 +18,17 @@ public class DynamicInt2ObjectMap<V> extends DynamicMap<Integer, V> implements I
 
     @Override
     public IntSet keySet() {
-        throw new UnsupportedOperationException();
+        return IntSets.EMPTY_SET;
     }
 
     @Override
     public ObjectCollection<V> values() {
-        throw new UnsupportedOperationException();
+        return ObjectLists.emptyList();
     }
 
     @Override
     public ObjectSet<Map.Entry<Integer, V>> entrySet() {
-        throw new UnsupportedOperationException();
+        return ObjectSets.emptySet();
     }
 
     @Override

common/src/main/java/org/embeddedt/modernfix/util/DynamicMap.java

@@ -4,6 +4,7 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
@@ -64,18 +65,18 @@ public class DynamicMap<K, V> implements Map<K, V> {
     @NotNull
     @Override
     public Set<K> keySet() {
-        throw new UnsupportedOperationException();
+        return Collections.emptySet();
     }
 
     @NotNull
     @Override
     public Collection<V> values() {
-        throw new UnsupportedOperationException();
+        return Collections.emptyList();
     }
 
     @NotNull
     @Override
     public Set<Entry<K, V>> entrySet() {
-        throw new UnsupportedOperationException();
+        return Collections.emptySet();
     }
 }