Union type for `error` disappears in typescript-fetch v0.10

[zaru]

Description

The union type for the error object returned by fetch has changed in typescript-fetch v0.10 and later versions.

Reproduction

I updated typescript-fetch to v0.10.1.

After the update, the type inference for the error object returned by fetch changed as follows:

Before v0.9.7

• const error: { message: string } | Record<string, never> | undefined

v0.10.0 and Later

• const error: { message: string } | undefined

OpenAPI YAML

I change the error response based on the type of error. For example, in the case of a 404 error, only a message is returned. For a 422 error, error messages are returned for each field.

# Partial YAML
      responses:
        '404':
          description: NotFound
          content:
            application/json:
              schema:
                type: object
                properties:
                  message:
                    type: string
                required:
                  - message
        '422':
          description: Bad parameters
          content:
            application/json:
              schema:
                title: ''
                type: object
                properties:
                  errors:
                    type: object
                    properties: {}
                required:
                  - errors

Expected result

It would be great if the error type could be the same as in previous versions:

const error: { message: string } | Record<string, never> | undefined

Checklist

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