A NackHandler handles when nack() is called in a user's AckReplyConsumer. Pub/Sub Lite does not
have a concept of 'nack'. When nack() is called in an AckReplyConsumerr, nack(message) is called
with the nacked message.
If the returned future is successful, the message is acknowledged. If the future fails, the
subscriber client will be failed. The default behavior is to immediately fail the client.
Methods
nack(PubsubMessage message)
public default ApiFuture<Void> nack(PubsubMessage message)