}
  }

  @Override
  final Iterator<E> elementIterator() {
    return new Itr<E>() {
      @Override
      @ParametricNullness
      E result(int entryIndex) {
        return backingMap.getKey(entryIndex);
      }
    };
  }

  @Override
  final Iterator<Entry<E>> entryIterator() {
    return new Itr<Entry<E>>() {
      @Override
      Entry<E> result(int entryIndex) {