Summary

When I tried to use ai-proxy multimodal input with azure provider, I got a 500 error with a log like:

[error] 147#0: *5356 [kong] init.lua:427 [ai-proxy] /usr/local/share/lua/5.1/kong/llm/proxy/handler.lua:458: code must be a number, client: 172.18.0.5, server: kong, request: "POST /test8-3-ai-proxy-gpt4o

I have just recognized the azure provider doesn't support multimodal input yet (well, actually, AOAI supports multimodal input after api-version 2024-06-01).

However, I found that the error handling path is broken and it raises unexpected errors.

This change is to fix to return 400 error properly for multimodal input with unsupported providers.

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #[issue number]