}

    @Override
    public @Nullable T pollFirst() {
      return standardPollFirst();
    }

    @Override
    public @Nullable T pollLast() {
      return standardPollLast();
    }

    @Override
    public SortedSet<T> headSet(T toElement) {
      return standardHeadSet(toElement);
    }

    @Override
    public SortedSet<T> tailSet(T fromElement) {

   * If you override {@link #descendingIterator} you may wish to override {@link #pollLast} to
   * forward to this implementation.
   */
  @CheckForNull
  protected E standardPollLast() {
    return Iterators.pollNext(descendingIterator());
  }

  @ParametricNullness
  protected E standardFirst() {
    return iterator().next();
  }

  @ParametricNullness