```

////

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.

以下のアプリケーションを例にしてみましょう:

```Python hl_lines="9"
{!../../docs_src/query_params_str_validations/tutorial001.py!}
```

クエリパラメータ `q` は `Optional[str]` 型で、`None` を許容する `str` 型を意味しており、デフォルトは `None` です。そのため、FastAPIはそれが必須ではないと理解します。

/// note | "備考"

FastAPIは、 `q` はデフォルト値が `=None` であるため、必須ではないと理解します。

`Optional[str]` における `Optional` はFastAPIには利用されませんが、エディターによるより良いサポートとエラー検出を可能にします。

///

## バリデーションの追加

{!> ../../docs_src/query_params_str_validations/tutorial001_py310.py!}
```

////

🔢 🔢 `q` 🆎 `Union[str, None]` (⚖️ `str | None` 🐍 3️⃣.1️⃣0️⃣), 👈 ⛓ 👈 ⚫️ 🆎 `str` ✋️ 💪 `None`, & 👐, 🔢 💲 `None`, FastAPI 🔜 💭 ⚫️ 🚫 ✔.

/// note

FastAPI 🔜 💭 👈 💲 `q` 🚫 ✔ ↩️ 🔢 💲 `= None`.

 `Union` `Union[str, None]` 🔜 ✔ 👆 👨‍🎨 🤝 👆 👍 🐕‍🦺 & 🔍 ❌.

///

## 🌖 🔬

//// tab | Python 3.10+

```Python
q: str | None = None
```

////

//// tab | Python 3.8+

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

////

Вот что мы получим, если обернём это в `Annotated`:

//// tab | Python 3.10+

```Python
q: Annotated[str | None] = None
```

////

//// tab | Python 3.8+

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

////

```

////

Der Query-Parameter `q` hat den Typ `Union[str, None]` (oder `str | None` in Python 3.10), was bedeutet, er ist entweder ein `str` oder `None`. Der Defaultwert ist `None`, also weiß FastAPI, der Parameter ist nicht erforderlich.

/// note | "Hinweis"

FastAPI weiß nur dank des definierten Defaultwertes `=None`, dass der Wert von `q` nicht erforderlich ist

        if (domainName != null) {
            String str;

            if (type == SID_TYPE_DOMAIN) {
                str = domainName;
            } else if (type == SID_TYPE_WKN_GRP ||
                        domainName.equals("BUILTIN")) {
                if (type == SID_TYPE_UNKNOWN) {
                    str = toString();
                } else {
                    str = acctName;
                }
            } else {

        annotation: Optional[Any] = None,
        alias: Optional[str] = None,
        alias_priority: Union[int, None] = _Unset,
        # TODO: update when deprecating Pydantic v1, import these types
        # validation_alias: str | AliasPath | AliasChoices | None
        validation_alias: Union[str, None] = None,
        serialization_alias: Union[str, None] = None,
        title: Optional[str] = None,
        description: Optional[str] = None,

def get_graphql_response(
    *,
    settings: Settings,
    query: str,
    after: Union[str, None] = None,
    category_id: Union[str, None] = None,
    discussion_number: Union[int, None] = None,
    discussion_id: Union[str, None] = None,
    comment_id: Union[str, None] = None,
    body: Union[str, None] = None,
) -> Dict[str, Any]:
    headers = {"Authorization": f"token {settings.input_token.get_secret_value()}"}

    description: Optional[str] = None
    content: Dict[str, MediaType]
    required: Optional[bool] = None


class Link(BaseModelWithConfig):
    operationRef: Optional[str] = None
    operationId: Optional[str] = None
    parameters: Optional[Dict[str, Union[Any, str]]] = None
    requestBody: Optional[Union[Any, str]] = None
    description: Optional[str] = None
    server: Optional[Server] = None

    return values


async def request_body_to_args(
    body_fields: List[ModelField],
    received_body: Optional[Union[Dict[str, Any], FormData]],
    embed_body_fields: bool,
) -> Tuple[Dict[str, Any], List[Dict[str, Any]]]:
    values: Dict[str, Any] = {}
    errors: List[Dict[str, Any]] = []
    assert body_fields, "request_body_to_args() should be called with fields"