Request body `{ x?: null; }` mishandled (regression from 0.16.0)

[andrew-stratyfy]

openapi-fetch version

0.17.0

Description

The attached reduced testcase compiles in 0.16.0 but fails in 0.17.0 with the following error:

Type error: Type '{ x?: null | undefined; }' is not assignable to type '{} & { x?: undefined; }'.
  Type '{ x?: null | undefined; }' is not assignable to type '{ x?: undefined; }'.
    Types of property 'x' are incompatible.
      Type 'null | undefined' is not assignable to type 'undefined'.
        Type 'null' is not assignable to type 'undefined'.

  42 | export const demo = async (body: components['schemas']['T']) => {
  43 |   const api = createClient<paths>();
> 44 |   return api.POST('/', { body });
     |                          ^
  45 | };
  46 |

I realize openapi-fetch is in maintenance mode, but it would be great if there's time to fix this or revert the troublesome code, since I'm currently stuck pinning to 0.16.0.

(You might ask why you'd want a body like this, but it makes more sense in the original code, where the type is more like { x?: null; y: Y } | { x: X; y?: null }.)

Thanks for all your work!

Reproduction

Minimal reproducer:

import createClient from 'openapi-fetch';

// Stripped down from a real openapi-typescript export
export interface paths {
  '/': {
    post: operations['demo'];
  };
}
export interface components {
  schemas: {
    T: {
      x?: null;
    };
  }
}
export interface operations {
  demo: {
    parameters: {
      query?: never;
      header?: never;
      path?: never;
      cookie?: never;
    };
    requestBody: {
      content: {
        'application/json': components['schemas']['T'];
      };
    };
    responses: {
      200: {
        headers: {
          [name: string]: unknown;
        };
        content: {
          'application/json': unknown;
        };
      };
    };
  };
}

export const demo = async (body: components['schemas']['T']) => {
  const api = createClient<paths>();
  return api.POST('/', { body });
};

Expected result

Compiles correctly. Note that the original code does something similar to the test case, where I pull the parameter's type straight from the schema, so I was very surprised when it didn't agree with itself. 😁

Extra

• I’m willing to open a PR (see CONTRIBUTING.md)