[FLINK-39952][Table SQL/Planner] Fix CallContextMock.isArgumentNull() to correctly handle optional arguments

[KenanAdel]

What is the purpose of the change

This pull request fixes CallContextMock to better match the CallContext contract when optional arguments are not provided in test scenarios.
Previously, some methods could access argument metadata and values using direct list lookups, which could lead to IndexOutOfBoundsException when a test declared optional arguments but did not provide corresponding entries. This change makes the mock handle missing optional arguments consistently and safely.

Brief change log

• Fixed isArgumentNull() to correctly handle missing optional arguments.
• Added bounds checks when accessing argument metadata and values in CallContextMock (including isArgumentLiteral() and getArgumentValue()).
• Prevented IndexOutOfBoundsException for optional arguments that are not provided.
• Preserved existing behavior for explicitly supplied arguments.

Verifying this change

This change is already covered by existing tests.
The affected behavior is exercised through the existing type inference test infrastructure that uses CallContextMock, including tests based on InputTypeStrategiesTestBase.

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

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: Claude- Opus 4.7

[flinkbot]

CI report:

• 0ad810d Azure: SUCCESS

Bot commands

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[KenanAdel]

@flinkbot run azure

[spuru9]

Can you make the PR Description as per the template provided in the repo.

[spuru9]

isArgumentLiteral() and getArgumentValue() still do a raw .get(pos). Not part of the ticket, but might as well guard it the same way while you're here

[KenanAdel]

@spuru9 Done. I've updated the PR description using the repository template and added consistent guard conditions to both isArgumentLiteral() and getArgumentValue(). Thanks for the review!

[MartijnVisser]

This is also a PR that I highly suspect that's not follow the AI contribution guidelines, and we can't merge it as is. Please follow the contribution guidelines as a whole before opening PRs @KenanAdel

[KenanAdel]

Thanks for the feedback I've reviewed the AI contribution guidelines and updated the PR to comply with them, including the required disclosure and PR template updates. I have verified the implementation and understand the design and code logic The PR is ready for review. @MartijnVisser