[BUG] empty type property on referenced enums

Created by: aghajani

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

When an enum is defined to be used later on multiple places using ref, the output Avro schema will put empty value on type property attribute of ref property. See samples below for better understanding.

openapi-generator version

lateset build from master and release: 5.3.1

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: Money event schema
  description: |
    Specification for the the MoneyEvent and all subtypes
  version: 0.1.0
servers: []
paths: {}

components:
  schemas:
    MoneyEventType:
      description: 'The kind of monetary transaction'
      type: string
      enum:
        - x1
        - x2

    MoneyEvent:
      description: 'A event describing some kind of monetary transaction'
      required:
        - eventType
      properties:
        eventType:
          $ref: '#/components/schemas/MoneyEventType'

Generation Details

generating models is enough to see invalid output for MoneyEvent:

{
  "namespace": "models",
  "type": "record",
  "doc": "A event describing some kind of monetary transaction",
  "name": "MoneyEvent",
  "fields": [
    {
      "name": "eventType",
      "type": ,
      "doc": ""
    }
  ]
}

Suggest a fix

The fix should be as simple as changing the mustache template for typeProperty in avro