code: public MultiMap merge(MultiMap multiMap)
      {
          MultiMap result = new MultiMap();
          result.map.putAll(this.map);
          result.map.putAll(multiMap.map);
          return result;
      }
docs: Merge the values in the specified map with the values in this map and return the results in a new map.
  @param multiMap The map to merge
  @return A new map containing the merged values