1011 null pointer when sending out response with no request metadata

[ana-vinogradova-camunda]

Description

This PR is related to this bug. This was fixed and backported to 8.4 and 8.3 this week.

The initial idea was to fix ZPT GrpcResponseWriter tryWriteResponse method to contain similar check that was introduced in Zeebe project:

    if (command.hasRequestMetadata()) {
      responseWriter.writeEventOnCommand(eventKey, SignalIntent.BROADCASTED, signalRecord, command);
    }

More details are available in this comment here. I am wondering if this is still valid as after the fix for this bug the response for broadcast signal events that have no corresponding request is not sent anymore:

This check in SignalBroadcastProcessor:

    if (command.hasRequestMetadata()) {
      responseWriter.writeEventOnCommand(eventKey, SignalIntent.BROADCASTED, signalRecord, command);
    }

is happening before GrpcResponseWriter is called.

I wonder if an extra check should still be added to GrpcResponseWriter? Do we have other scenarios when we don't have request metadata available? I will add the check if so 👍

What is in this draft PR:

• Unit test that verifies that no response is sent for broadcast signal event that have no corresponding request
• More details are available in separate commit messages

Related issues

closes #1011

Definition of Done

Not all items need to be done depending on the issue and the pull request.

Code changes:

• [ ] The changes are backwards compatibility with previous versions
• [ ] If it fixes a bug then PRs are created to backport the fix

Testing:

• [ ] There are unit/integration tests that verify all acceptance criterias of the issue
• [ ] New tests are written to ensure backwards compatibility with further versions
• [ ] The behavior is tested manually

Documentation:

• [ ] Javadoc has been written
• [ ] The documentation is updated

[github-actions[bot]]

Test Results

 50 files  ±0   50 suites  ±0   2m 25s :stopwatch: +34s 136 tests +1  136 :white_check_mark: +1  0 :zzz: ±0  0 :x: ±0  432 runs  +3  432 :white_check_mark: +3  0 :zzz: ±0  0 :x: ±0 

Results for commit ea3bbb74. ± Comparison against base commit 66657e54.

[ana-vinogradova-camunda]

@tmetzke thank you for the suggestion 👍

I think that it is a good idea to fix this on the response writer-level as well while working on this bug. I am not sure where this issue might happen, but I'll investigate.

I will address other comments as well 👍

[ana-vinogradova-camunda]

Closing as decided on different implementation.