class User(BaseModel):
    username: str


def get_current_user(oauth_header: str | None = Security(api_key)):
    if oauth_header is None:
        return None
    user = User(username=oauth_header)
    return user


@app.get("/users/me")
def read_current_user(current_user: User = Depends(get_current_user)):
    if current_user is None:
        return {"msg": "Create an account first"}
    else:
        return current_user

例如，你可以宣告某個值可以是 `str` 或 `None`：

```python
from typing import Union


def say_hi(name: Union[str, None]):
        print(f"Hi {name}!")
```

在 `typing` 中也有用 `Optional` 宣告某個值可以是 `None` 的速記法。

以下是我個人（非常主觀）的建議：

* 🚨 避免使用 `Optional[SomeType]`
* 改為 ✨ 使用 `Union[SomeType, None]` ✨。

    return "fakehashed" + password


oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")


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


class UserInDB(User):
    hashed_password: str


def get_user(db, username: str):
    if username in db:
        user_dict = db[username]

    username: str
    password: str
    email: EmailStr
    full_name: str | None = None


class UserOut(BaseModel):
    username: str
    email: EmailStr
    full_name: str | None = None


class UserInDB(BaseModel):
    username: str
    hashed_password: str
    email: EmailStr
    full_name: str | None = None


def fake_password_hasher(raw_password: str):
    return "supersecret" + raw_password

@SuppressWarnings("checkstyle:InterfaceIsType")
public interface Language extends ExtensibleEnum {

    /**
     * The "none" language. It is not versioned, family is same to itself, and compatible with itself only.
     * In turn, every {@link Language} implementation must be compatible with {@code NONE} language.
     */
    Language NONE = language("none");

    /**
     * The "resources" language. This is used for files such as images to provide in the output.

		}
		// Once is set and we are here means error was already
		// printed once.
		if once {
			return
		}
		// once not set, check if same error occurred 3 times in
		// a row, then make sure we print it to call attention.
		if m[err.Error()] > 2 {
			peersLogAlwaysIf(ctx, fmt.Errorf("Following error has been printed %d times.. %w", m[err.Error()], err))
			// Reduce the count to introduce further delay in printing

                return "auto";
            }

            @Override
            public String getSsoType() {
                return "none";
            }
        });
        final OsddHelper osddHelper = new OsddHelper();
        osddHelper.setOsddPath("osdd/none.xml");
        osddHelper.init();
        assertFalse(osddHelper.hasOpenSearchFile());
    }

    @Test
    public void test_init_disabled() {

    github_repository: str
    github_token: SecretStr
    deploy_url: str | None = None
    commit_sha: str
    run_id: int
    state: Literal["pending", "success", "error"] = "pending"


class LinkData(BaseModel):
    previous_link: str
    preview_link: str
    en_link: str | None = None


def main() -> None:
    logging.basicConfig(level=logging.INFO)
    settings = Settings()

        "item": {
            "name": "Foo",
            "price": 50.5,
            "description": None,
            "tax": None,
        },
        "user": {"username": "Dave", "full_name": None},
    }


def test_post_body_no_data(client: TestClient):
    response = client.put("/items/5", json=None)
    assert response.status_code == 422
    assert response.json() == {
        "detail": [
            {

            "axisLabel": "",
            "axisPlacement": "auto",
            "barAlignment": 0,
            "drawStyle": "line",
            "fillOpacity": 10,
            "gradientMode": "none",
            "hideFrom": {
              "legend": false,
              "tooltip": false,
              "viz": false
            },
            "insertNulls": false,
            "lineInterpolation": "linear",