Steps to reproduce

1. Install and configure the module (as in the example configuration: https://docs.magnolia-cms.com/magnolia-rabbitmq/rmq-setup-example.html)
2. Set improper server public key (/server/activation@publicKey) on the public instance
3. Publish a new/updated page
4. Observe author instance logs
5. Set the proper server public key (/server/activation@publicKey) on the public instance
6. Publish the second new/updated page
7. Observe author instance logs

Expected results

No errors, the first page is marked as not published and the second page is marked as published 

Actual results

Publisher instance errors. Both pages are not marked as published

Workaround

The custom class which inherit from ConfirmationConsumer class with bugfix

Cause

(based on decompiled source, line numbers may be wrong)
In ConfirmationConsumer class on line 80 you call 

ackMap.keys(); 

which, when ackMap is null, throws NullPointerException. I suggest changing it to:

if(ackMap != null) {
  Iterator<String> keysIt = ackMap.keys();
  if (keysIt.hasNext()) {
    ... 

(see attached screens for more detailed info)

ackMap is null when message body is '[]', which is ok-ish when public instance exception thrown