* #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may wish to
   * override {@link #higher} to forward to this implementation.
   */
  protected @Nullable E standardHigher(@ParametricNullness E e) {
    return Iterators.getNext(tailSet(e, false).iterator(), null);
  }

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

  /**

   * #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may wish to
   * override {@link #higher} to forward to this implementation.
   */
  protected @Nullable E standardHigher(@ParametricNullness E e) {
    return Iterators.getNext(tailSet(e, false).iterator(), null);
  }

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

  /**