code: @Beta
    public static <E> SortedMultiset<E> unmodifiableSortedMultiset(SortedMultiset<E> sortedMultiset) {
      // it's in its own file so it can be emulated for GWT
      return new UnmodifiableSortedMultiset<E>(checkNotNull(sortedMultiset));
    }
docs: Returns an unmodifiable view of the specified sorted multiset. Query operations on the returned
  multiset "read through" to the specified multiset, and attempts to modify the returned multiset
  result in an {@link UnsupportedOperationException}.
  
  <p>The returned multiset will be serializable if the specified multiset is serializable.
  
  @param sortedMultiset the sorted multiset for which an unmodifiable view is to be generated
  @return an unmodifiable view of the multiset
  @since 11.0