* Collection#stream} on a collection).
   *
   * <p><b>Note:</b> the earlier in the chain you can switch to {@code Stream} usage (ideally not
   * going through {@code FluentIterable} at all), the more performant and idiomatic your code will
   * be. This method is a transitional aid, to be used only when really necessary.
   *
   * @since 21.0
   */
  public final Stream<E> stream() {