[FLINK-37610] Check if orderBy keys exists before accessing

[bvarghese1]

What is the purpose of the change

• Avoid IndexOutOfBoundsException when an OverAgg query is used without specifying an Order By clause

Brief change log

• If ORDER BY clause is not specified in an Over agg, it would lead to IndexOutOfBoundsException
• This commit adds a check to ensure orderby fields exists before accessing them

Verifying this change

This change added tests and can be verified as follows:

• Added test that validates OverAgg query can be used without an ORDER BY clause

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, 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? (not applicable)

[flinkbot]

CI report:

• ecae441 Azure: SUCCESS

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[snuyanzin]

out of curiosity: is there a case when it is not empty and over.logicWindow.groups is empty?

[bvarghese1]

No that can't happen since order by is specified inside the over clause

[snuyanzin]

then I don't understand why do we need both !groups.isEmpty && !groups.get(0).orderKeys.getFieldCollations.isEmpty in condition?
isn't just one of them enough?

[bvarghese1]

Ideally this one condition should be enough i.e. !groups.get(0).orderKeys.getFieldCollations.isEmpty but the condition !groups.isEmpty is just a safety check. We can remove the safety check since there will always be 1 group.