https://developer.paciellogroup.com/blog/2018/03/focus-visible-and-backwards-compatibility/\n[tabindex=\"-1\"]:focus:not(:focus-visible) {\n  outline: 0 !important;\n}\n\n\n// Content grouping\n//\n// 1. Add the correct box sizing in Firefox.\n// 2. Show the overflow in Edge and IE.\n\nhr {\n  box-sizing: content-box; // 1\n  height: 0; // 1\n  overflow: visible; // 2\n}\n\n\n//\n// Typography\n//\n\n// Remove top margins from headings\n//\n// By default, `<h1>`-`<h6>` all receive top and bottom margins. We nuke...

```

...calling the path `/items/invalidnone` will raise an error, because `None` is not a valid type for the `response_model` declared with `Item`.

You could also be implicitly returning `None` without realizing, for example:

```Python
from fastapi import FastAPI
from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: Optional[float] = None