code: @SuppressWarnings("unchecked")
    public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(E e1, E e2) {
      return copyOf(Ordering.natural(), Arrays.asList(e1, e2));
    }
docs: Returns an immutable sorted multiset containing the given elements sorted by their natural
  ordering.
  
  @throws NullPointerException if any element is null