### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

The `chatgpt/gpt-5.4` throw exception when stream is `false`. It work fine with other `chatgpt/*` model.

### Steps to Reproduce

1. Try send something like this. ```json { "model": "gpt-5.4", "stream": false, "messages": [ { "role": "system", "content": "Say Hello to the user" }, { "role": "user", "content": "Hello" } ] } ``` 2. Then you will always get this: ``` { "error": { "message": "litellm.APIConnectionError: APIConnectionError: ChatgptException - Unknown items in responses API response: []. Received Model Group=gpt-5.4\nAvailable Model Group Fallbacks=None", "type": null, "param": null, "code": "500" } } ```

### Relevant log output

```shell litellm-1 | raise e litellm-1 | File "/app/.venv/lib/python3.13/site-packages/litellm/utils.py", line 1892, in wrapper_async litellm-1 | result = await original_function(*args, **kwargs) litellm-1 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ litellm-1 | File "/app/.venv/lib/python3.13/site-packag…