validation_alias: Union[str, None] = None,
        serialization_alias: Union[str, None] = None,
        title: Optional[str] = None,
        description: Optional[str] = None,
        gt: Optional[float] = None,
        ge: Optional[float] = None,
        lt: Optional[float] = None,
        le: Optional[float] = None,
        min_length: Optional[int] = None,
        max_length: Optional[int] = None,

        Doc(
            """
            'Whitelist' validation step. The parameter field will be the single one
            allowed by the alias or set of aliases defined.
            """
        ),
    ] = None,
    serialization_alias: Annotated[
        Union[str, None],
        Doc(
            """
            'Blacklist' validation step. The vanilla parameter field will be the

            "overridden": "app",
        }


def test_merged_no_return_lifespans_return_none() -> None:
    @asynccontextmanager
    async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
        yield

    @asynccontextmanager
    async def router_lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
        yield

    router = APIRouter(lifespan=router_lifespan)
    app = FastAPI(lifespan=lifespan)

        summary: Optional[str] = None,
        description: Optional[str] = None,
        response_description: str = "Successful Response",
        responses: Optional[Dict[Union[int, str], Dict[str, Any]]] = None,
        deprecated: Optional[bool] = None,
        name: Optional[str] = None,
        methods: Optional[Union[Set[str], List[str]]] = None,
        operation_id: Optional[str] = None,

```

////

The query parameter `q` is of type `Union[str, None]` (or `str | None` in Python 3.10), that means that it's of type `str` but could also be `None`, and indeed, the default value is `None`, so FastAPI will know it's not required.

/// note

FastAPI will know that the value of `q` is not required because of the default value `= None`.

The `Union` in `Union[str, None]` will allow your editor to give you better support and detect errors.

    name: str = Field(index=True)
    age: int | None = Field(default=None, index=True)


class Hero(HeroBase, table=True):
    id: int | None = Field(default=None, primary_key=True)
    secret_name: str


class HeroPublic(HeroBase):
    id: int


class HeroCreate(HeroBase):
    secret_name: str


class HeroUpdate(HeroBase):
    name: str | None = None
    age: int | None = None
    secret_name: str | None = None

                """
            ),
        ] = None,
        scheme_name: Annotated[
            Optional[str],
            Doc(
                """
                Security scheme name.

                It will be included in the generated OpenAPI (e.g. visible at `/docs`).
                """
            ),
        ] = None,
        scopes: Annotated[

    dependant: Dependant,
    body: Optional[Union[Dict[str, Any], FormData]] = None,
    background_tasks: Optional[StarletteBackgroundTasks] = None,
    response: Optional[Response] = None,
    dependency_overrides_provider: Optional[Any] = None,
    dependency_cache: Optional[Dict[Tuple[Callable[..., Any], Tuple[str]], Any]] = None,
    async_exit_stack: AsyncExitStack,
    embed_body_fields: bool,
) -> SolvedDependency:

    name: Optional[str] = None
    call: Optional[Callable[..., Any]] = None
    request_param_name: Optional[str] = None
    websocket_param_name: Optional[str] = None
    http_connection_param_name: Optional[str] = None
    response_param_name: Optional[str] = None
    background_tasks_param_name: Optional[str] = None
    security_scopes_param_name: Optional[str] = None
    security_scopes: Optional[List[str]] = None

from fastapi import FastAPI, Header
from pydantic import BaseModel

app = FastAPI()


class CommonHeaders(BaseModel):
    host: str
    save_data: bool
    if_modified_since: str | None = None
    traceparent: str | None = None
    x_tag: list[str] = []


@app.get("/items/")
async def read_items(headers: CommonHeaders = Header()):