Invalid response object is generated for cyclical schemas

[RobertCraigie]

Context

Given this OpenAPI spec which contains a circular schema definition:

openapi: 3.0.2
paths:
  /pet:
    get:
      responses:
        200:
          description: ok
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/return'
components:
  schemas:
    return:
      type: object
      properties:
        child:
          $ref: '#/components/schemas/return'
          nullable: true
      required:
        - child

Current Behavior

Prism responds with

{
  "child": {
    "$ref": null
  }
}

Expected Behavior

It should instead respond with

{
  "child": null
}

Possible Workaround/Solution

Explicitly setting an example for the child property to null

Steps to Reproduce

1. Start a mock server for the given spec
2. Run curl -sXGET http://127.0.0.1:4010/pet

Environment

• Version used: 4.14.1
• Environment name and version (e.g. Chrome 39, node.js 5.4): nodejs v19.6.1
• Operating System and version (desktop or mobile): MacOS M1
• Link to your environment/workspace/project:

[chohmann]

@RobertCraigie the spec you provided is invalid. $ref cannot have any other sibling properties. When you remove the invalid nullable: true from the spec you provided, Prism correctly mocks the response.

To represent the child property either being the return schema or null, you would need to use a oneOf.