Backport to branch(3) : Fix NPE that occurs with DELETE w/o clustering key

[feeblefakie]

This is an automated backport of the following:

• Original PR: Fix NPE that occurs with DELETE w/o clustering key #2981
• Backported commit: 316229b

Please merge this PR after all checks have passed.

[gemini-code-assist]

Summary of Changes

Hello @feeblefakie, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request backports a critical fix to address a NullPointerException (NPE) that previously occurred during DELETE operations when no clustering key was specified. The changes involve refactoring the CommitMutationComposer and RollbackMutationComposer classes to ensure that Delete and Get operations are constructed robustly, by conditionally applying the clustering key only when it is present. This prevents the system from attempting to use a null clustering key, thereby eliminating the NPE and improving the stability of database operations.

Highlights

• NPE Fix for Delete Operations: The core logic for composing Delete operations in CommitMutationComposer was updated to correctly handle cases where no clustering key is provided, preventing potential NullPointerExceptions.
• Rollback Logic Enhancement: Similar adjustments were made in RollbackMutationComposer to ensure Delete and Get operations are constructed safely when clustering keys are absent, maintaining transactional integrity during rollbacks.
• Comprehensive Test Coverage: New unit tests were added across CommitMutationComposerTest and RollbackMutationComposerTest to specifically validate the behavior of Put and Delete operations when clustering keys are not present, ensuring the fix is robust.

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[gemini-code-assist]

Code Review

This pull request backports a fix for a NullPointerException that could occur when handling DELETE operations without a clustering key. The changes in CommitMutationComposer and RollbackMutationComposer correctly address this by using the builder pattern to conditionally set the clustering key, avoiding passing null to the builder methods. The change in RollbackMutationComposer.getLatestResult also fixes a similar issue for Get operations. The accompanying tests are well-written and cover the cases without clustering keys.

I have one suggestion to improve the code's consistency and readability in RollbackMutationComposer.

[gemini-code-assist]

For consistency with other changes in this PR and for better readability, you can use Optional.ofNullable with ifPresent to conditionally set the clustering key. This makes the null-handling more explicit and fluent.

    Optional.ofNullable(clusteringKey).ifPresent(getBuilder::clusteringKey);