code: void addAll( HashMultimap<K, V> m ) {
          if( m == this ) {
              return;
          }
          for( Entry<K, List<V>> entry : m.map.entrySet() ) {
              K key = entry.getKey();
              List<V> rules = map.get( key );
              if( rules == null ) {
                  rules = new ArrayList<>();
                  map.put( key, rules );
              }
              for( V value : entry.getValue() ) {
                  if( !rules.contains( value ) ) {
                      rules.add( value );
                  }
              }
          }
      }
docs: Add all values of the mappings from the specified map to this map.
  
  @param m
  mappings to be stored in this map