NullPointerException upon writing error response

[remcowesterhoud]

Describe the bug

The ErrorResponseWriter tried to write an error response, but the errorCode was null.

To Reproduce

I don't know

Expected behavior

No NPE is thrown.

Log/Stacktrace

https://console.cloud.google.com/errors/detail/CNr_jurZ9ZLCzAE;service=zeebe;time=P7D?project=camunda-cloud-240911

Full Stacktrace

 java.lang.NullPointerException: error code
	at java.util.Objects.requireNonNull(Unknown Source) ~[?:?]
	at io.camunda.zeebe.util.EnsureUtil.ensureNotNull(EnsureUtil.java:20) ~[zeebe-util-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.broker.transport.ErrorResponseWriter.tryWriteResponse(ErrorResponseWriter.java:161) ~[zeebe-broker-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.broker.transport.AsyncApiRequestHandler.lambda$handleRequest$1(AsyncApiRequestHandler.java:114) ~[zeebe-broker-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.scheduler.future.FutureContinuationRunnable.run(FutureContinuationRunnable.java:28) ~[zeebe-scheduler-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.scheduler.ActorJob.invoke(ActorJob.java:94) ~[zeebe-scheduler-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.scheduler.ActorJob.execute(ActorJob.java:45) ~[zeebe-scheduler-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.scheduler.ActorTask.execute(ActorTask.java:119) ~[zeebe-scheduler-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.scheduler.ActorThread.executeCurrentTask(ActorThread.java:106) ~[zeebe-scheduler-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.scheduler.ActorThread.doWork(ActorThread.java:87) ~[zeebe-scheduler-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT]
	at io.camunda.zeebe.scheduler.ActorThread.run(ActorThread.java:198) ~[zeebe-scheduler-8.1.0-SNAPSHOT.jar:8.1.0-SNAPSHOT] 

Environment:

• Zeebe Version: latest SNAPSHOT

[remcowesterhoud]

@oleschoenburg I'm a bit swarmed currently so I didn't do a very deep dive into this NPE. What I quickly saw is that it originates from the AsyncApiRequestHandler. It seems like you've created this a few days ago. Maybe you can have a quick look if you already see something wrong.

[oleschoenburg]

AsyncApiRequestHandler is mostly a rename, it existed before as ApiRequestHandler.

Looks like the command api handler returned the error writer but didn't set a error code, which should not be possible 😬

[oleschoenburg]

Yikes, looks like I made a mess out of AsyncApiRequestHandler 🤦

We are re-using the readers and writers which is not safe since handlers are async.

[pihme]

Appears in benchmark that was created after the fix was merged:
https://console.cloud.google.com/errors/detail/CNr_jurZ9ZLCzAE;service=zeebe;version=medic-cw-32-be18e23b78-benchmark;time=P7D?project=zeebe-io