code: 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;
      }
docs: Triggers key loading if needed on the map key loader with the
  {@link Role#SENDER} or {@link Role#SENDER_BACKUP} role if this
  partition does not have any ongoing key loading task.
  
  @return a future representing pending completion of the key loading task