Le paramètre de requête `q` a pour type `Union[str, None]` (ou `str | None` en Python 3.10), signifiant qu'il est de type `str` mais pourrait aussi être égal à `None`, et bien sûr, la valeur par défaut est `None`, donc **FastAPI** saura qu'il n'est pas requis.

/// note

**FastAPI** saura que la valeur de `q` n'est pas requise grâce à la valeur par défaut `= None`.

            """
        ),
    ] = _Unset,
    # TODO: update when deprecating Pydantic v1, import these types
    # validation_alias: str | AliasPath | AliasChoices | None
    validation_alias: Annotated[
        Union[str, None],
        Doc(
            """
            'Whitelist' validation step. The parameter field will be the single one
            allowed by the alias or set of aliases defined.

    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"

        self,
        *,
        flows: Annotated[
            Union[OAuthFlowsModel, Dict[str, Dict[str, Any]]],
            Doc(
                """
                The dictionary of OAuth2 flows.
                """
            ),
        ] = OAuthFlowsModel(),
        scheme_name: Annotated[
            Optional[str],
            Doc(
                """
                Security scheme name.

    with pytest.raises(RuntimeError, match=multipart_incorrect_install_error):
        app = FastAPI()

        @app.post("/")
        async def root(username: str = Form(), password: str = Form()):
            return username  # pragma: nocover


def test_incorrect_multipart_installed_form_file(monkeypatch):
    monkeypatch.setattr("python_multipart.__version__", "0.0.12")

{!../../docs_src/python_types/tutorial009.py!}
```

Using `Optional[str]` instead of just `str` will let the editor help you detect errors where you could be assuming that a value is always a `str`, when it could actually be `None` too.

`Optional[Something]` is actually a shortcut for `Union[Something, None]`, they are equivalent.

This also means that in Python 3.10, you can use `Something | None`:

//// tab | Python 3.10+

| 매개변수 | 타입 | 설명 |
|----------|------|-------|
| `title` | `str` | API의 제목입니다. |
| `summary` | `str` | API에 대한 짧은 요약입니다. <small>OpenAPI 3.1.0, FastAPI 0.99.0부터 사용 가능</small> |
| `description` | `str` | API에 대한 짧은 설명입니다. 마크다운을 사용할 수 있습니다. |
| `version` | `string` | API의 버전입니다. OpenAPI의 버전이 아닌, 여러분의 애플리케이션의 버전을 나타냅니다. 예: `2.5.0` |
| `terms_of_service` | `str` | API 이용 약관의 URL입니다. 제공하는 경우 URL 형식이어야 합니다. |

    SpliteratorTester.of(
            () ->
                CollectSpliterators.flatMap(
                    Arrays.spliterator(new String[] {"abc", "", "de", "f", "g", ""}),
                    (String str) -> str.isEmpty() ? null : charactersOf(str).spliterator(),
                    Spliterator.SIZED | Spliterator.DISTINCT | Spliterator.NONNULL,
                    7))
        .expect('a', 'b', 'c', 'd', 'e', 'f', 'g');
  }

|------------|------|-------------|
| `title` | `str` | O título da API. |
| `summary` | `str` | Um breve resumo da API. <small>Disponível desde OpenAPI 3.1.0, FastAPI 0.99.0.</small> |
| `description` | `str` | Uma breve descrição da API. Pode usar Markdown. |
| `version` | `string` | A versão da API. Esta é a versão da sua aplicação, não do OpenAPI. Por exemplo, `2.5.0`. |

    public static String stripLeadingAndTrailingQuotes(String str) {
        requireNonNull(str, "str");
        final int length = str.length();
        if (length > 1
                && str.startsWith("\"")
                && str.endsWith("\"")
                && str.substring(1, length - 1).indexOf('"') == -1) {
            str = str.substring(1, length - 1);
        }
        return str;
    }

    @Nonnull