code: public PubsubFuture<List<ReceivedMessage>> pull(final String project, final String subscription,
                                                    final boolean returnImmediately, final int maxMessages) {
      return pull(Subscription.canonicalSubscription(project, subscription), returnImmediately, maxMessages);
    }
docs: Pull a batch of messages.
  
  @param project           The Google Cloud project.
  @param subscription      The subscription to pull from.
  @param returnImmediately {@code true} to return immediately if the queue is empty. {@code false} to wait for at
  least one message before returning.
  @param maxMessages       Maximum number of messages to return in batch.
  @return a future that is completed with a list of received messages.