app = FastAPI()
router_a = APIRouter()
router_a_a = APIRouter()
router_a_b_override = APIRouter()  # Overrides default class
router_b_override = APIRouter()  # Overrides default class
router_b_a = APIRouter()
router_b_a_c_override = APIRouter()  # Overrides default class again


@app.get("/")
def get_root():
    return {"msg": "Hello World"}

        '"dom_id": "#swagger-ui"' in response.text
    ), "default configs should be preserved"
    assert "presets: [" in response.text, "default configs should be preserved"
    assert (
        "SwaggerUIBundle.presets.apis," in response.text
    ), "default configs should be preserved"
    assert (
        "SwaggerUIBundle.SwaggerUIStandalonePreset" in response.text
    ), "default configs should be preserved"
    assert (

            assert param.annotation == router_param.annotation
            assert param.annotation == app_param.annotation
            assert param.default == router_param.default

Sprich:

```Python
q: Union[str, None] = Query(default=None)
```

... macht den Parameter optional, mit dem Defaultwert `None`, genauso wie:

```Python

Таким образом:

```Python
q: Union[str, None] = Query(default=None)
```

...делает параметр необязательным со значением по умолчанию `None`, также как это делает:

```Python

                        },
                    },
                }
            },
            "/query/list-default": {
                "get": {
                    "summary": "Get Query List Default",
                    "operationId": "get_query_list_default_query_list_default_get",
                    "parameters": [
                        {
                            "name": "device_ids",

        def query_example(
            data: Union[str, None] = Query(
                default=None,
                example="query1",
            ),
        ):
            return data

    @app.get("/query_examples/")
    def query_examples(
        data: Union[str, None] = Query(
            default=None,
            examples=["query1", "query2"],
        ),
    ):
        return data

                            "required": False,
                            "schema": {
                                "title": "Skip",
                                "type": "integer",
                                "default": 0,
                            },
                            "name": "skip",
                            "in": "query",
                        },
                        {

                            "required": False,
                            "schema": {
                                "title": "Skip",
                                "type": "integer",
                                "default": 0,
                            },
                            "name": "skip",
                            "in": "query",
                        },
                        {

{!../../../docs_src/query_params_str_validations/tutorial002.py!}
```

Note que substituímos o valor padrão de `None` para `Query(default=None)`, o primeiro parâmetro de `Query` serve para o mesmo propósito: definir o valor padrão do parâmetro.

Então:

```Python
q: Union[str, None] = Query(default=None)
```

...Torna o parâmetro opcional, da mesma maneira que:

```Python
q: Union[str, None] = None
```