code: public PartitionReducer<Partition<T>> getOrCreateReducer()
     {
        Node node = childNode.getOrCreate("reducer");
        PartitionReducer<Partition<T>> reducer = new PartitionReducerImpl<Partition<T>>(this, "reducer", childNode, node);
        return reducer;
     }
docs: If not already created, a new <code>reducer</code> element with the given value will be created.
  Otherwise, the existing <code>reducer</code> element will be returned.
  @return  a new or existing instance of <code>PartitionReducer<Partition<T>></code>