code: public boolean addAllValues(MultiMap<V> map) {
          boolean merged = false;
  
          if ((map == null) || (map.isEmpty())) {
              // done
              return merged;
          }
  
          for (Map.Entry<String, List<V>> entry : map.entrySet()) {
              String name = entry.getKey();
              List<V> values = entry.getValue();
  
              if (this.containsKey(name)) {
                  merged = true;
              }
  
              this.addValues(name, values);
          }
  
          return merged;
      }
docs: Merge values.
  
  @param map the map to overlay on top of this one, merging together values
  if needed.
  @return true if an existing key was merged with potentially new values,
  false if either no change was made, or there were only new keys.