EventManager.java

public int addQueryListener(QueryListener queryListener) {
  Query query = queryListener.getQuery();

  QueryListenersInfo queryInfo = queries.get(query);
  boolean firstListen = queryInfo == null;
  if (firstListen) {
    // QueryListenersInfo is only created if no identical query is registered
    queryInfo = new QueryListenersInfo();
    queries.put(query, queryInfo);
  }
  ...
}