^{Originally posted by akishichinibu September 26, 2024}
https://typespec.io/playground?c=c2NhbGFyIE15U3RyIGV4dGVuZHMgc3RyaW5nOwoKbW9kZWwgQSB7CiAgeDrHJnwgbnVsbAp9Cg%3D%3D&e=%40typespec%2Fopenapi3&options=%7B%7D

Consider the following TypeSpec definition:

scalar MyStr extends string;

model A {
  x: MyStr | null;
}

openapi: 3.0.0
info:
  title: (title)
  version: 0.0.0
tags: []
paths: {}
components:
  schemas:
    A:
      type: object
      required:
        - x
      properties:
        x:
          oneOf:
            - $ref: '#/components/schemas/MyStr'
          nullable: true
    MyStr:
      type: string

This generates the following OpenAPI specification, which violates the Redoc rule spec.

The `type` field must be defined when the `nullable` field is used.

In this case, the error occurs because the nullable field is used without defining the type explicitly within the oneOf clause, which Redoc requires for proper validation.

How can I fix this?