code: private Service createServiceHook(String flowletName, Iterable<ConsumerSupplier<?>> consumerSuppliers,
                                      AtomicReference<FlowletProgramController> controller) {
      final List<String> streams = Lists.newArrayList();
      for (ConsumerSupplier<?> consumerSupplier : consumerSuppliers) {
        QueueName queueName = consumerSupplier.getQueueName();
        if (queueName.isStream()) {
          streams.add(queueName.getSimpleName());
        }
      }
  
      // If no stream, returns a no-op Service
      if (streams.isEmpty()) {
        return new AbstractService() {
          @Override
          protected void doStart() {
            notifyStarted();
          }
  
          @Override
          protected void doStop() {
            notifyStopped();
          }
        };
      }
      return new FlowletServiceHook(flowletName, streams, controller);
    }
docs: Create a initializer to be executed during the flowlet driver initialization.