[FLINK-21592][table-planner-blink] RemoveSingleAggregateRule fails du…

[lirui-apache]

…e to nullability mismatch

What is the purpose of the change

Fix query plan failure due to RemoveSingleAggregateRule.

Brief change log

• Don't assume nullable value in RemoveSingleAggregateRule::onMatch
• Add test case

Verifying this change

Added test case

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

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? NA

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Last check on commit 830b573 (Fri May 28 09:06:14 UTC 2021)

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[KurtYoung]

Could you find another place to add the test? Adding this to TableEnvironmentTest doesn't sound right to me.

[lirui-apache]

I have moved the test to a dedicated class RemoveSingleAggregateRuleTest. Hopefully that makes things clearer.

[KurtYoung]

LGTM