}

  @Override
  public @Nullable Entry<K, V> pollFirstEntry() {
    return Iterators.pollNext(entryIterator());
  }

  @Override
  public @Nullable Entry<K, V> pollLastEntry() {
    return Iterators.pollNext(descendingEntryIterator());
  }

  @Override
  @ParametricNullness
  public K firstKey() {
    Entry<K, V> entry = firstEntry();

  }

  @Override
  public @Nullable Entry<K, V> pollFirstEntry() {
    return Iterators.pollNext(entryIterator());
  }

  @Override
  public @Nullable Entry<K, V> pollLastEntry() {
    return Iterators.pollNext(descendingEntryIterator());
  }

  @Override
  @ParametricNullness
  public K firstKey() {
    Entry<K, V> entry = firstEntry();

   * override {@link #iterator} you may wish to override {@link #pollFirst} to forward to this
   * implementation.
   */
  protected @Nullable E standardPollFirst() {
    return Iterators.pollNext(iterator());
  }

  @Override
  public @Nullable E pollLast() {
    return delegate().pollLast();
  }

  /**