code: public static <E> Collector<E, ?, ImmutableSortedMultiset<E>> toImmutableSortedMultiset(
        Comparator<? super E> comparator) {
      return toImmutableSortedMultiset(comparator, Function.identity(), e -> 1);
    }
docs: Returns a {@code Collector} that accumulates the input elements into a new {@code
  ImmutableMultiset}. Elements are sorted by the specified comparator.
  
  <p><b>Warning:</b> {@code comparator} should be <i>consistent with {@code equals}</i> as
  explained in the {@link Comparator} documentation.
  
  @since 21.0