@Override
    public boolean contains(@Nullable Object o) {
      return Maps.containsEntryImpl(delegate(), o);
    }

    @Override
    public boolean containsAll(Collection<?> c) {
      return standardContainsAll(c);
    }

    @Override
    public boolean removeAll(Collection<?> c) {
      return standardRemoveAll(c);
    }

    @Override
    public boolean retainAll(Collection<?> c) {

        return object != null && Collections2.safeContains(delegate, object);
      }

      @Override
      public boolean containsAll(Collection<?> collection) {
        return standardContainsAll(collection);
      }

      @Override
      public boolean remove(@Nullable Object object) {
        return object != null && Collections2.safeRemove(delegate, object);
      }

      @Override