@Override
 public void sendNotification(Notification notification, Set<String> tags) {
   for (INotificationHub hub : hubs.values()) {
     hub.sendNotification(notification, tags);
   }
 }
 @Override
 public void sendNotification(Notification notification, String tagExpression) {
   for (INotificationHub hub : hubs.values()) {
     hub.sendNotification(notification, tagExpression);
   }
 }
 @Override
 public void sendNotification(Notification notification) {
   for (INotificationHub hub : hubs.values()) {
     hub.sendNotification(notification);
   }
 }