fix: AzureOpenAIChatGenerator.to_dict() crashes when response_format is a plain dict

[rautaditya2606]

Related Issues

Closes #12406

Proposed Changes

• Added the missing isinstance(response_format, type) guard before calling issubclass(response_format, BaseModel) in AzureOpenAIChatGenerator.to_dict().
• Added a parametrized regression test (test_to_dict_with_dict_response_format) in test/components/generators/chat/test_azure.py covering both dictionary-based structured output formats: {"type": "json_object"} and {"type": "json_schema", ...}.
• Added release note in releasenotes/notes/fix-azure-chat-generator-to-dict-response-format-1b844d5eaadcbd81.yaml.

How did you test it?

hatch -e test run pytest test/components/generators/chat/test_azure.py

30 passed, 5 skipped in 0.57s.

hatch -e test run pytest test/components/generators/chat/test_azure.py -k test_to_dict_with_dict_response_format

2 passed, 34 deselected in 0.19s.

Notes for the reviewer

• Root cause: issubclass() expects a class (type) as its first argument. When response_format is provided in generation_kwargs as a plain dictionary (standard for OpenAI JSON mode and Structured Outputs), evaluating issubclass(dict_instance, BaseModel) raises an unhandled TypeError: issubclass() arg 1 must be a class during to_dict() serialization.

• This change aligns AzureOpenAIChatGenerator.to_dict() with the existing pattern in OpenAIChatGenerator.to_dict() (haystack/components/generators/chat/openai.py) and AzureOpenAIResponsesGenerator.to_dict() (haystack/components/generators/chat/azure_responses.py).

• Reproducer:

    from haystack.components.generators.chat import AzureOpenAIChatGenerator

    generator = AzureOpenAIChatGenerator(
        azure_endpoint="https://example-resource.azure.openai.com/",
        generation_kwargs={"response_format": {"type": "json_object"}},
    )

    # Before fix -> TypeError: issubclass() arg 1 must be a class
    # After fix  -> serializes successfully with response_format preserved
    generator.to_dict()

Checklist

• Read contributors guidelines and code of conduct
• Updated related issue
• Added unit tests and updated docstrings
• Used conventional commit type in PR title (fix: AzureOpenAIChatGenerator.to_dict() crashes when response_format is a plain dict)
• Documented code
• Added release note (releasenotes/notes/fix-azure-chat-generator-to-dict-response-format-1b844d5eaadcbd81.yaml)
• Run pre-commit hooks and fixed any issues

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Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/components/generators/chat
azure.py
Project Total

This report was generated by python-coverage-comment-action

[sjrl]

@bogdankostic I can take this review!

[sjrl]

Thanks!