code: public static <K, V> SetMultimap<K, V> synchronizedSetMultimap(SetMultimap<K, V> multimap) {
      return Synchronized.setMultimap(multimap, null);
    }
docs: Returns a synchronized (thread-safe) {@code SetMultimap} backed by the specified multimap.
  
  <p>You must follow the warnings described in {@link #synchronizedMultimap}.
  
  <p>The returned multimap will be serializable if the specified multimap is serializable.
  
  @param multimap the multimap to be wrapped
  @return a synchronized view of the specified multimap