fix: fix azure open-4o-08-06 when enable json schema cant process content = ""

[liujiamingtiny]

Summary

The bug caused by Azure model changes first occurred on November 18, 2024. When using the Azure OpenAI GPT-4o-08-06 model with JSON schema format output, if a tool is invoked and the assistant message content is an empty string, the model fails to respond properly, ultimately resulting in a 500 error. To ensure compatibility, it is necessary to detect when the assistant message involves a tool invocation and replace an empty message content with None to enable proper responses.

Screenshots

debug wiht azure py code

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after:

debug with dify backend code:

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after：

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods