code: public void addVirtualSelectNode(Integer originalId, Integer virtualId, List<String> selectedNames) {
  
  		if (virtualSelectNodes.containsKey(virtualId)) {
  			throw new IllegalStateException("Already has virtual select node with id " + virtualId);
  		}
  
  		virtualSelectNodes.put(virtualId,
  				new Tuple2<Integer, List<String>>(originalId, selectedNames));
  	}
docs: Adds a new virtual node that is used to connect a downstream vertex to only the outputs
  with the selected names.
  
  <p>When adding an edge from the virtual node to a downstream node the connection will be made
  to the original node, only with the selected names given here.
  
  @param originalId ID of the node that should be connected to.
  @param virtualId ID of the virtual node.
  @param selectedNames The selected names.