code: public static <E> Builder<E> orderedBy(Comparator<E> comparator) {
      return new Builder<E>(comparator);
    }
docs: Returns a builder that creates immutable sorted multisets with an explicit comparator. If the
  comparator has a more general type than the set being generated, such as creating a {@code
  SortedMultiset<Integer>} with a {@code Comparator<Number>}, use the {@link Builder} constructor
  instead.
  
  @throws NullPointerException if {@code comparator} is null