[BUG] [haskell-http-client] Using a schema reference for an optional form parameter of a request body results in broken code

Created by: typetetris

Bug Report Checklist

• Provided a broken spec.
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?

Description

Using a schema reference for an optional form parameter of a request body results in broken code.

I expected compiling code.

openapi-generator version

From Commit 6c5621d9 (HEAD of master at the moment)

OpenAPI declaration file content or url

openapi: 3.0.2
info:
  title: Example
  description: Example to demonstrate issues with optional parameters for haskell-http-client
  contact:
    name: example
    url: https://www.example.example
    email: example@test.test
  license:
    name: whateveryouneed
    url: https://www.example.example
  version: 0.0.1
servers: []
paths:
  /example:
    post:
      tags:
        - example
      description: Example
      operationId: exampleOp
      requestBody:
        description: example
        required: true
        content:
          'application/x-www-form-urlencoded':
            schema:
              type: object
              properties:
                example:
                  $ref: '#/components/schemas/Example'
      responses:
        '204':
          description: Success
components:
  schemas:
    "Example":
      title: ExampleEnum
      type: string
      enum:
        - "Value1"
        - "Value2"
        - "Value3"
      description: ''

Command line used for generation

openapi-generator-cli generate -o test -i example.yaml -g haskell-http-client

Steps to reproduce

cd test
cabal build

Related issues/PRs

none to my knowledge

Suggest a fix

pr incoming. There is a completely arbitrary if condition in the code, with no else branch and the else case leaves some vendor extensions thingies uninitialised.