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