docs: protected void fireKNNsInserted(DBIDs insertions, DBIDs updates) {
      KNNChangeEvent e = new KNNChangeEvent(this, KNNChangeEvent.Type.INSERT, insertions, updates);
      Object[] listeners = listenerList.getListenerList();
      for(int i = listeners.length - 2; i >= 0; i -= 2) {
        if(listeners[i] == KNNListener.class) {
          ((KNNListener) listeners[i + 1]).kNNsChanged(e);
        }
      }
    }