if (Ordering.natural().equals(comparator)) {
      return (ImmutableSortedMultiset<E>) RegularImmutableSortedMultiset.NATURAL_EMPTY_MULTISET;
    } else {
      return new RegularImmutableSortedMultiset<>(comparator);
    }
  }

  ImmutableSortedMultiset() {}

  @Override
  public final Comparator<? super E> comparator() {