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"
    )

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"
    )

from pydantic import BaseModel

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")


class User(BaseModel):
    username: str
    email: Union[str, None] = None
    full_name: Union[str, None] = None
    disabled: Union[bool, None] = None


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

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")


class User(BaseModel):
    username: str
    email: Union[str, None] = None
    full_name: Union[str, None] = None
    disabled: Union[bool, None] = None


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

```

Note que substituímos o valor padrão de `None` para `Query(default=None)`, o primeiro parâmetro de `Query` serve para o mesmo propósito: definir o valor padrão do parâmetro.

Então:

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

...Torna o parâmetro opcional, da mesma maneira que:

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

Mas o declara explicitamente como um parâmetro de consulta.

                        "description": IsDict(
                            {
                                "title": "Description",
                                "anyOf": [{"type": "string"}, {"type": "null"}],
                            }
                        )
                        | IsDict(
                            # TODO: remove when deprecating Pydantic v1

                        },
                        "repeat_at": IsDict(
                            {
                                "title": "Repeat At",
                                "anyOf": [
                                    {"type": "string", "format": "time"},
                                    {"type": "null"},
                                ],
                            }

        if (value == null) {
            buf.append("null");
        } else if (value instanceof LocalDateTime) {
            final String format =
                    ((LocalDateTime) value).atZone(ZoneId.systemDefault()).withZoneSameInstant(ZoneId.of("UTC")).format(ISO_8601_FORMATTER);
            buf.append('"').append(StringEscapeUtils.escapeJson(format)).append('"');
        } else if (value instanceof String[]) {

        end
        handler -->> client: HTTP error response
    end

    operation ->> client: Return response to client
    Note over client,operation: Response is already sent, can't change it anymore
    opt Tasks
        operation -->> tasks: Send background tasks
    end
    opt Raise other exception
        tasks -->> tasks: Handle exceptions in the background task code
    end
```

                            "required": False,
                            "deprecated": True,
                            "schema": IsDict(
                                {
                                    "anyOf": [
                                        {
                                            "type": "string",
                                            "minLength": 3,