docs: public void backupAck(long id, Address from, int topologyId) {
        BaseAckTarget ackTarget = collectorMap.get(id);
        if (ackTarget instanceof SingleKeyCollector) {
           ((SingleKeyCollector) ackTarget).backupAck(topologyId, from);
        } else if (ackTarget instanceof MultiTargetCollectorImpl) {
           ((MultiTargetCollectorImpl) ackTarget).backupAck(topologyId, from);
        }
     }