code: public void sendToUsers(String topicURI, Object event, Set<String> eligibleUsers) {
  
  		Set<String> eligibleSessionIds = null;
  		if (eligibleUsers != null && !eligibleUsers.isEmpty()) {
  			eligibleSessionIds = new HashSet<>(eligibleUsers.size());
  
  			for (String user : eligibleUsers) {
  				for (SimpSession session : this.simpUserRegistry.getUser(user)
  						.getSessions()) {
  					eligibleSessionIds.add(session.getId());
  				}
  			}
  		}
  
  		this.eventMessenger.sendTo(topicURI, event, eligibleSessionIds);
  	}
docs: Send an {@link EventMessage} to every client that is currently subscribed to the
  given topicURI and are listed in the eligibleUsers set. If no user of the provided
  set is subscribed to the topicURI nothing happens.
  
  @param topicURI the name of the topic
  @param event the payload of the {@link EventMessage}
  @param eligibleUsers only the users listed here will receive the EVENT message. If
  null or empty nobody receives the message.