I think `Union[SomeType, None]` is more explicit about what it means.

It's just about the words and names. But those words can affect how you and your teammates think about the code.

As an example, let's take this function:

```Python hl_lines="1  4"
{!../../../docs_src/python_types/tutorial009c.py!}
```

* 📝 Add External Link: FastAPI application monitoring made easy. PR [#10917](https://github.com/tiangolo/fastapi/pull/10917) by [@tiangolo](https://github.com/tiangolo).
* ✨ Generate automatic language names for docs translations. PR [#5354](https://github.com/tiangolo/fastapi/pull/5354) by [@jakul](https://github.com/jakul).

cff-version: 1.2.0
title: FastAPI
message: >-
  If you use this software, please cite it using the
  metadata from this file.
type: software
authors:
  - given-names: Sebastián
    family-names: Ramírez
    email: ******@****.***
identifiers:
repository-code: 'https://github.com/tiangolo/fastapi'
url: 'https://fastapi.tiangolo.com'
abstract: >-

## Documenting webhooks with **FastAPI** and OpenAPI

With **FastAPI**, using OpenAPI, you can define the names of these webhooks, the types of HTTP operations that your app can send (e.g. `POST`, `PUT`, etc.) and the request **bodies** that your app would send.

As code duplication increments the chances of bugs, security issues, code desynchronization issues (when you update in one place but not in the others), etc.

And these models are all sharing a lot of the data and duplicating attribute names and types.

We could do better.

We can declare a `UserBase` model that serves as a base for our other models. And then we can make subclasses of that model that inherit its attributes (type declarations, validation, etc).

## Nested Models

Each attribute of a Pydantic model has a type.

But that type can itself be another Pydantic model.

So, you can declare deeply nested JSON "objects" with specific attribute names, types and validations.

All that, arbitrarily nested.

### Define a submodel

For example, we can define an `Image` model:

=== "Python 3.10+"

    ```Python hl_lines="7-9"

## Shortcut to remember the names

Let's see the previous example again:

```Python hl_lines="6"
{!../../../docs_src/response_status_code/tutorial001.py!}
```

`201` is the status code for "Created".

You will get completion in code you might even consider impossible before. As for example, the `price` key inside a JSON body (that could have been nested) that comes from a request.

No more typing the wrong key names, coming back and forth between docs, or scrolling up and down to find if you finally used `username` or `user_name`.

### Short

app = FastAPI()


@app.get("/items/")
async def read_items():
    return [{"item_id": "Foo"}]


def use_route_names_as_operation_ids(app: FastAPI) -> None:
    """
    Simplify operation IDs so that generated API clients have simpler function
    names.

    Should be called only after all routes have been added.
    """
    for route in app.routes:
        if isinstance(route, APIRoute):

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