```

デフォルト値`None`を`Query(default=None)`に置き換える必要があるので、`Query`の最初の引数はデフォルト値を定義するのと同じです。

なので:

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

...を以下と同じようにパラメータをオプションにします:

```Python
q: Optional[str] = None
```

しかし、これはクエリパラメータとして明示的に宣言しています。

!!! info "情報"
    FastAPIは以下の部分を気にすることを覚えておいてください:

    ```Python
    = None
    ```

    もしくは:

    minimum: Optional[float] = None
    exclusiveMinimum: Optional[float] = None
    maxLength: Optional[int] = Field(default=None, ge=0)
    minLength: Optional[int] = Field(default=None, ge=0)
    pattern: Optional[str] = None
    maxItems: Optional[int] = Field(default=None, ge=0)
    minItems: Optional[int] = Field(default=None, ge=0)
    uniqueItems: Optional[bool] = None
    maxContains: Optional[int] = Field(default=None, ge=0)

from pydantic import BaseModel


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


app = FastAPI()


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item, q: Union[str, None] = None):
    result = {"item_id": item_id, **item.dict()}
    if q:
        result.update({"q": q})

app = FastAPI()


class Image(BaseModel):
    url: str
    name: str


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None
    tags: set[str] = set()
    image: Image | None = None


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item):
    results = {"item_id": item_id, "item": item}

app = FastAPI()


class Image(BaseModel):
    url: HttpUrl
    name: str


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None
    tags: set[str] = set()
    image: Image | None = None


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item):
    results = {"item_id": item_id, "item": item}

        dependencies: Optional[List["Dependant"]] = None,
        security_schemes: Optional[List[SecurityRequirement]] = None,
        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,

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


class User(BaseModel):
    username: str
    full_name: str | None = None


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item, user: User, importance: int = Body()):

le(e,t){for(var n,r,i,o,a,s,u,l=[],c=0,f=e.length;c<f;c++)(r=e[c]).style&&(n=r.style.display,t?("none"===n&&(l[c]=Y.get(r,"display")||null,l[c]||(r.style.display="")),""===r.style.display&&ae(r)&&(l[c]=(u=a=o=void 0,a=(i=r).ownerDocument,s=i.nodeName,(u=ue[s])||(o=a.body.appendChild(a.createElement(s)),u=E.css(o,"display"),o.parentNode.removeChild(o),"none"===u&&(u="block"),ue[s]=u)))):"none"!==n&&(l[c]="none",Y.set(r,"display",n)));for(c=0;c<f;c++)null!=l[c]&&(e[c].style.display=l[c]);return e}E.fn....

app = FastAPI()


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: float = 10.5
    tags: List[str] = []


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The bartenders", "price": 62, "tax": 20.2},
    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}

from pydantic import BaseModel

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")


class User(BaseModel):
    username: str
    email: str | None = None
    full_name: str | None = None
    disabled: bool | None = None


def fake_decode_token(token):
    return User(
        username=token + "fakedecoded", email="******@****.***", full_name="John Doe"
    )