* explained in the {@link Comparator} documentation.
   *
   * @since 21.0
   */
  public static <E> Collector<E, ?, ImmutableSortedMultiset<E>> toImmutableSortedMultiset(
      Comparator<? super E> comparator) {
    return toImmutableSortedMultiset(comparator, Function.identity(), e -> 1);
  }

  /**
   * Returns a {@code Collector} that accumulates elements into an {@code ImmutableSortedMultiset}