[FLINK-9458] Unable to recover from job failure on YARN with NPE

[yanghua]

What is the purpose of the change

This pull request fixed a NPE when recover job on YARN

Brief change log

• *Add non-null judge in the expression *

Verifying this change

This change is already covered by existing tests, such as CoLocationConstraintTest.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[yanghua]

cc @zentol

[kkrugler]

I'm wondering why, now, we're encountering cases where the sharedSlot value is null? Seems like this could be caused by a deeper problem somewhere, so just adding the null check is masking something else that should be fixed.

Also, seems like we'd want a test case to verify the failure (pre-fix) and then appropriate behavior with the fix.

[kkrugler]

One other note - I ran into this problem, but it wasn't on YARN. It was running locally (via unit test triggered in Eclipse).

[tillrohrmann]

Could you please close this PR @yanghua. It is now subsumed by #6119.

[yanghua]

@tillrohrmann OK, closing...