docs: public LinkedList<PlanNode> getPathTo( PlanNode descendant ) {
          assert descendant != null;
          LinkedList<PlanNode> stack = new LinkedList<PlanNode>();
          PlanNode node = descendant;
          while (node != this) {
              stack.addFirst(node);
              node = node.getParent();
              assert node != null : "The supplied node is not a descendant of this node";
          }
          stack.addFirst(this);
          return stack;
      }