fix: Null cases for openai prompt and embeddings

[ranadeepsingh]

Related Issues/PRs

#2444 - caused the bug and divergence
#2456 - suggested partial fix

What changes are proposed in this pull request?

Fix bug in OpenAIEmbedding when input is None/Null it was giving Null Pointer Exception.
Revamped and changed OpenAIEmbedding and OpenAIPrompt to return None/Null whne input is None/Null regardless of returnUsage is True or False.

• Add tests for null case so this bug doesn't occur again

How is this patch tested?

• I have written tests (not required for typo or doc fix) and confirmed the proposed feature/bug-fix/change works.

Does this PR change any dependencies?

• No. You can skip this section.
• Yes. Make sure the dependencies are resolved correctly, and list changes here.

Does this PR add a new feature? If so, have you added samples on website?

• No. You can skip this section.
• Yes. Make sure you have added samples following below steps.

1. Find the corresponding markdown file for your new feature in website/docs/documentation folder.
   Make sure you choose the correct class estimators/transformers and namespace.
2. Follow the pattern in markdown file and add another section for your new API, including pyspark, scala (and .NET potentially) samples.
3. Make sure the DocTable points to correct API link.
4. Navigate to website folder, and run yarn run start to make sure the website renders correctly.
5. Don't forget to add <!--pytest-codeblocks:cont--> before each python code blocks to enable auto-tests for python samples.
6. Make sure the WebsiteSamplesTests job pass in the pipeline.

[github-actions]

Hey @ranadeepsingh 👋!
Thank you so much for contributing to our repository 🙌.
Someone from SynapseML Team will be reviewing this pull request soon.

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[ranadeepsingh]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull request overview

This PR fixes a NullPointerException bug in OpenAIEmbedding and OpenAIPrompt transformers when input is null. The fix ensures both transformers return null output when input is null, regardless of the returnUsage parameter setting.

Key Changes:

• Modified OpenAIPrompt to wrap output in when(parsedCol.isNotNull, ...) for both usage-enabled and usage-disabled modes
• Modified OpenAIEmbedding to wrap output in when(responseCol.isNotNull, ...) for both usage-enabled and usage-disabled modes
• Added comprehensive tests for null input handling in both transformers with both returnUsage=true and returnUsage=false

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
cognitive/src/main/scala/com/microsoft/azure/synapse/ml/services/openai/OpenAIPrompt.scala	Added null-safety checks in withUsageColumn method to return null when parsedCol is null, for both struct (with usage) and plain (without usage) output cases
cognitive/src/main/scala/com/microsoft/azure/synapse/ml/services/openai/OpenAIEmbedding.scala	Added null-safety checks in transform method to return null when responseCol is null, for both struct (with usage) and plain vector output cases, plus imported when function
cognitive/src/test/scala/com/microsoft/azure/synapse/ml/services/openai/OpenAIPromptSuite.scala	Added two new tests for null input handling with both returnUsage=false and returnUsage=true; refactored test names to remove "Gpt 4" references and cleaned up unused test fixtures
cognitive/src/test/scala/com/microsoft/azure/synapse/ml/services/openai/OpenAIEmbeddingsSuite.scala	Added two new tests for null input handling with both returnUsage=false and returnUsage=true

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.35%. Comparing base (bfa8c46) to head (13bb3eb).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2457      +/-   ##
==========================================
+ Coverage   84.34%   84.35%   +0.01%     
==========================================
  Files         335      335              
  Lines       17723    17729       +6     
  Branches     1616     1621       +5     
==========================================
+ Hits        14948    14956       +8     
+ Misses       2775     2773       -2     

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