code: public List<V> getMultiples(final K parent) {
          return new ArrayList<>(Option.of(this.prototypes.get(parent))
                                       .map(Map::values)
                                       .getOrElse(Collections.emptyList()));
      }
docs: @param parent The parent instance of all the nodes sought
  
  @return All the multiple-type nodes under the given parent instance, or an empty list if there are none.