code: public static <K, V> SetMultimap<K, V> newSetMultimap(Multimap<K, V> multimap) {
          return new SetMultimap<K, V>(HashMap::new, HashSet::new, multimap);
      }
docs: Creates a new instance backed by a {@link HashMap} and {@link HashSet}. All key-value mappings are copied from the input multimap. If any
  collection of values in the input multimap contains duplicate elements, these are removed in the constructed multimap.
  
  @param multimap