/** @since 12.0 */
  @Override
  @CheckForNull
  public E ceiling(E e) {
    return Iterables.<@Nullable E>getFirst(tailSet(e, true), null);
  }

  /** @since 12.0 */
  @GwtIncompatible // NavigableSet
  @Override
  @CheckForNull
  public E higher(E e) {
    return Iterables.<@Nullable E>getFirst(tailSet(e, false), null);
  }

  @Override
  public E first() {
    return iterator().next();
  }

    }
  }

  /**
   * Returns the next element in {@code iterator} or {@code defaultValue} if the iterator is empty.
   * The {@link Iterables} analog to this method is {@link Iterables#getFirst}.
   *
   * @param defaultValue the default value to return if the iterator is empty
   * @return the next element of {@code iterator} or the default value
   * @since 7.0
   */
  @ParametricNullness