code: public void sendMessageTo(VertexKey target, Message m) {
  		outValue.f0 = target;
  		outValue.f1 = m;
  		out.collect(outValue);
  	}
docs: Sends the given message to the vertex identified by the given key. If the target vertex does not exist,
  the next superstep will cause an exception due to a non-deliverable message.
  
  @param target The key (id) of the target vertex to message.
  @param m The message.