OpenAPI generator regression

api.yaml

swagger: "2.0"
info:
  version: "3"
  title: API

host: localhost:8443
basePath: /api

schemes:
  - https
consumes:
  - application/json
produces:
  - application/json

paths:

  /reproduce-bug:
    get:
      summary: Reproduce the bug
        
      responses:
        200:
          description: Success
          schema:
            $ref: "#/definitions/GetResponse"

definitions:
  ObjectMap:
    type: object
    required:
      - default
    properties:
      default:
        type: string
    additionalProperties:
      type: object

  GetResponse:
    type: object
    properties:
      data:
        $ref: "#/definitions/ObjectMap"
        description: Key value pairs of data