code: private static SpoutNode getDRPCSpoutNode(Collection<Node> g) {
          for(Node n: g) {
              if(n instanceof SpoutNode) {
                  SpoutNode.SpoutType type = ((SpoutNode) n).type;
                  if(type==SpoutNode.SpoutType.DRPC) {
                      return (SpoutNode) n;
                  }
              }
          }
          return null;
      }
docs: returns null if it's not a drpc group