code: public List<PlanNode> findAllAtOrBelow( Traversal order,
                                              Type typeToFind ) {
          return findAllAtOrBelow(order, EnumSet.of(typeToFind));
      }
docs: Find all of the nodes of the specified type that are at or below this node.
  
  @param order the order to traverse; may not be null
  @param typeToFind the type of node to find; may not be null
  @return the collection of nodes that are at or below this node that all have the supplied type; never null but possibly
  empty