If you are using `response_model` with some type that doesn't include `None` but the function is returning `None`, it will now raise an internal server error, because you are returning invalid data that violates the contract in `response_model`. Before this release it would allow breaking that contract returning `None`.

For example, if you have an app like this:

```Python
from fastapi import FastAPI

- Kube-apiserver: fixes scale subresource patch handling to avoid returning unnecessary 409 Conflict error to clients ([#90342](https://github.com/kubernetes/kubernetes/pull/90342), [@liggitt](https://github.com/liggitt)) [SIG Apps, Autoscaling and Testing]