`response_model`, converting any data as necessary to generate the
                    corresponding JSON. But if the data in the object returned is not
                    valid, that would mean a violation of the contract with the client,
                    so it's an error from the API developer. So, FastAPI will raise an
                    error and return a 500 error code (Internal Server Error).

This means that now, if you set a value in a context variable before `yield`, the value would still be available after `yield` (as you would intuitively expect). And it also means that you can reset the context variable with a token afterwards.

For example, this works correctly now:

```Python