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