docs: public void removeNotificationHandler(String serviceName, NotificationHandler handler){
          if(handler == null || serviceName == null || serviceName.isEmpty()){
              throw new IllegalArgumentException();
          }
  
          synchronized(notificationHandlers){
              if(notificationHandlers.containsKey(serviceName)){
                  List<NotificationHandler> list = notificationHandlers.get(serviceName);
                  if(list.contains(handler)){
                      list.remove(handler);
                  }
                  if(list.size() == 0){
                      notificationHandlers.remove(serviceName);
                  }
              }
          }
      }