[BUG][Java][Spring] OpenApi contract with objects having no properties and a parent get wrong generated equals()

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Whenever an OpenApi model specification has an allOf, but does not contain any properties of it's own, the openAPI generator fails calling super.equals().

openapi-generator version

7.0.0

OpenAPI declaration file content or url

SomeObject:
  allOf:
    - $ref: 'parent-object.yml#/ParentObject'
  type: object
  description: |
    some description

ParentObject:
  type: object
  discriminator:
    propertyName: some_type
  description: |
    some more description.
  required:
    - property_1
    - value
  properties:
    property_1:
      $ref: 'property-1.yml#/Property1'
    value:
      type: string
      description: Some other description
    some_type:
      type: string

Generation Details

Steps to reproduce

When running openApi generator for objects using allOf, but not having properties of it's own, call to super.equals is missing.

Related issues/PRs

Suggest a fix

Always call super.equals when using allOf.

Start by reproducing the issue with the provided SomeObject and ParentObject OpenAPI declarations and inspect the generated Java model equals() methods. Confirm that an allOf model with no own properties compares its parent correctly by calling the parent equality behavior; done means the generated output handles this case without the reported failure.