Build issues with NextJS14 type checking fails for null values

[devraj]

I have an endpoint written in python using fastapi which exposes a standard OAuth token endpoint, which uses a OAuth2 Password Form model, expected to be passed in as form data.

@router.post(
    "/token",
    summary="Provides an endpoint for login via email and password",
)
async def login_for_auth_token(
    form_data: OAuth2PasswordRequestForm = Depends(),
    session: AsyncSession = Depends(get_async_session)
) -> Token:
    """ Attempt to authenticate a user and issue JWT token

    If the user does not exists or the password is incorrect
    then an exception is raised which returns a 4xx response.

    """
    user = await User.get_by_email(
        session,
        form_data.username
    )

See fastapi example for context.

I have used the same setup with frameworks like remix and not encountered any issues, however we are moving to NextJS14 and When I use orval to generate the client to consume the token endpoint eslint complains with the following:

./api/auth/auth.ts:171:41
Type error: Argument of type 'BodyLoginForAuthTokenGrantType' is not assignable to parameter of type 'string'.
  Type 'null' is not assignable to type 'string'.

  169 |   const formUrlEncoded = new URLSearchParams();
  170 |   if (bodyLoginForAuthToken.grant_type !== undefined) {
> 171 |     formUrlEncoded.append("grant_type", bodyLoginForAuthToken.grant_type);
      |                                         ^
  172 |   }
  173 |   formUrlEncoded.append("username", bodyLoginForAuthToken.username);
  174 |   formUrlEncoded.append("password", bodyLoginForAuthToken.password);

adding a check for those values to be !==null makes eslint happy:

  if (bodyLoginForAuthToken.grant_type !== undefined && bodyLoginForAuthToken.grant_type !== null) {
    formUrlEncoded.append("grant_type", bodyLoginForAuthToken.grant_type);
  }

I was wonder if this should be something orval generates? I can get around it by asking eslint to ignore the file, it would be nice to get someone else's thoughts on this.

Thank you for time.

---

Node version: v21.1.0
OS: macOS 14
Framework: NextJS 14.0.1
orval: 6.19.1

[melloware]

Interesting it sounds like a bug ? Weird that it's saying can't assign Null to string but it's not NULL it's a String. Open to a fix if you want to investigate further.

[devraj]

As in lodge an issue or you'd like me to investigate the code and provide a pull request?

[melloware]

Investigate and PR

[devraj]

I intend to get to this in the next couple of days