if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=409, detail="Item already exists")
    fake_db[item.id] = item

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=400, detail="Item already exists")
    fake_db[item.id] = item

from fastapi import Depends, FastAPI
from fastapi.testclient import TestClient

app = FastAPI()


async def user_exists(user_id: int):
    return True


@app.get("/users/{user_id}", dependencies=[Depends(user_exists)])
async def read_users(user_id: int):
    pass


client = TestClient(app)


def test_read_users():
    response = client.get("/users/42")
    assert response.status_code == 200, response.text

</div>

This means that it will **always have a value**, it's just that sometimes the value could be `None` (or `null` in JSON).

That means that, clients using your API don't have to check if the value exists or not, they can **assume the field will always be there**, but just that in some cases it will have the default value of `None`.

@app.command()
def new_lang(lang: str = typer.Argument(..., callback=lang_callback)):
    """
    Generate a new docs translation directory for the language LANG.
    """
    new_path: Path = Path("docs") / lang
    if new_path.exists():
        typer.echo(f"The language was already created: {lang}")
        raise typer.Abort()
    new_path.mkdir()
    new_config_path: Path = Path(new_path) / mkdocs_name

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=400, detail="Item already exists")
    fake_db[item.id] = item

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item.id in fake_db:
        raise HTTPException(status_code=400, detail="Item already exists")
    fake_db[item.id] = item

            "title": "The Foo ID Stealers",
            "description": "There goes my stealer",
        },
    )
    assert response.status_code == 400

            "title": "The Foo ID Stealers",
            "description": "There goes my stealer",
        },
    )
    assert response.status_code == 409

            "title": "The Foo ID Stealers",
            "description": "There goes my stealer",
        },
    )
    assert response.status_code == 400