# if flag is False, at this point the function will implicitly return None
```

If you have *path operations* using `response_model` that need to be allowed to return `None`, make it explicit in `response_model` using `Union[Something, None]`:

```Python
from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

class Item(BaseModel):
    name: str

inal":{"@defaults font-variant-numeric":{},"--tw-ordinal":"ordinal","font-variant-numeric":t},".slashed-zero":{"@defaults font-variant-numeric":{},"--tw-slashed-zero":"slashed-zero","font-variant-numeric":t},".lining-nums":{"@defaults font-variant-numeric":{},"--tw-numeric-figure":"lining-nums","font-variant-numeric":t},".oldstyle-nums":{"@defaults font-variant-numeric":{},"--tw-numeric-figure":"oldstyle-nums","font-variant-numeric":t},".proportional-nums":{"@defaults font-variant-numeric":{},"-...