previous = current = next;
      next = next.next;
      nextIndex++;
      return current;
    }

    @Override
    public void remove() {
      checkForConcurrentModification();
      checkState(current != null, "no calls to next() since the last call to remove()");
      if (current != next) { // after call to next()
        previous = current.previous;
        nextIndex--;

        if (!hasNext) {
            throw new NoSuchElementException();
        }
        hasNext = false;
        return value;
    }

    @Override
    public void remove() {
        throw new ClUnsupportedOperationException("remove");
    }

   * {@code get(null)}, {@code keySet().contains(null)} or {@code remove(null)}.
   */
  ALLOWS_NULL_KEY_QUERIES,
  ALLOWS_NULL_KEYS(ALLOWS_NULL_KEY_QUERIES),
  /**
   * The map does not throw {@code NullPointerException} on calls such as {@code
   * containsValue(null)}, {@code values().contains(null)} or {@code values().remove(null)}.
   */
  ALLOWS_NULL_VALUE_QUERIES,
  ALLOWS_NULL_VALUES(ALLOWS_NULL_VALUE_QUERIES),

  }

  public void testRemove() {
    TestMap map = new TestMap();
    map.put("foo", 1);
    assertFalse(map.remove("foo", 2));
    assertFalse(map.remove("bar", 1));
    assertEquals(Integer.valueOf(1), map.get("foo"));
    assertTrue(map.remove("foo", 1));
    assertTrue(map.isEmpty());
  }

  public void testReplace() {
    TestMap map = new TestMap();
    map.put("foo", 1);

/**
 * The reason why a cached entry was removed.
 *
 * @author Charles Fry
 * @since 10.0
 */
@GwtCompatible
public enum RemovalCause {
  /**
   * The entry was manually removed by the user. This can result from the user invoking {@link
   * Cache#invalidate}, {@link Cache#invalidateAll(Iterable)}, {@link Cache#invalidateAll()}, {@link
   * Map#remove}, {@link ConcurrentMap#remove}, or {@link Iterator#remove}.
   */
  EXPLICIT {

    }

    public void mymodifyProperty(String propertyName) {
        registerModifiedProperty(propertyName);
    }

    public void mymodifyPropertyCancel(String propertyName) {
        __modifiedProperties.remove(propertyName);
    }

    public void clearModifiedInfo() {
        __modifiedProperties.clear();
    }

    public boolean hasModification() {
        return !__modifiedProperties.isEmpty();
    }

    }

    public void mymodifyProperty(String propertyName) {
        registerModifiedProperty(propertyName);
    }

    public void mymodifyPropertyCancel(String propertyName) {
        __modifiedProperties.remove(propertyName);
    }

    public void clearModifiedInfo() {
        __modifiedProperties.clear();
    }

    public boolean hasModification() {
        return !__modifiedProperties.isEmpty();
    }

    Set<Feature<?>> inverseFeatures = new HashSet<>(mapFeatures);

    boolean nullKeys = inverseFeatures.remove(MapFeature.ALLOWS_NULL_KEYS);
    boolean nullValues = inverseFeatures.remove(MapFeature.ALLOWS_NULL_VALUES);

    if (nullKeys) {
      inverseFeatures.add(MapFeature.ALLOWS_NULL_VALUES);
    }
    if (nullValues) {

        return delegate().iterator();
      }

      @Override
      public int size() {
        return delegate().size();
      }

      @Override
      public boolean remove(Object o) {
        return delegate().remove(o);
      }

      @Override
      public void clear() {
        delegate().clear();
      }
    };
  }

  @Override
  public @Nullable Entry<K, V> firstEntry() {

    throw new UnsupportedOperationException();
  }

  @CanIgnoreReturnValue
  @Override
  public final boolean remove(@Nullable Object element) {
    return remove(element, 1) > 0;
  }

  @CanIgnoreReturnValue
  @Override
  public int remove(@Nullable Object element, int occurrences) {
    throw new UnsupportedOperationException();
  }

  @CanIgnoreReturnValue
  @Override