docs: private Future triggerLoading() {
          if (keyLoadFinished.isDone()) {
              keyLoadFinished = new LoadFinishedFuture();
  
              // side effect -> just trigger load on SENDER_BACKUP ID SENDER died
              execService.execute(MAP_LOAD_ALL_KEYS_EXECUTOR, () -> {
                  // checks if loading has finished and triggers loading in case SENDER died and SENDER_BACKUP took over.
                  Operation op = new TriggerLoadIfNeededOperation(mapName);
                  opService.<Boolean>invokeOnPartition(SERVICE_NAME, op, mapNamePartition)
                          // required since loading may be triggered after migration
                          // and in this case the callback is the only way to get to know if the key load finished or not.
                          .andThen(loadingFinishedCallback());
              });
          }
          return keyLoadFinished;
      }