[BUG] openapi-generator-cli doesnt validate empty enums

[nghiahsgs]

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Please differentiate the bug

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Please also check if the bug is already known before you open a new bug.

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🐛 Bug Report:

Describe the bug

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Steps to Reproduce

Steps to reproduce the behavior:

1. Create sample file test.yaml

openapi: 3.0.3
info:
  title: Simple API with Enum
  description: A simple API to demonstrate enum usage in OpenAPI.
  version: 1.0.0

paths:
  /items:
    get:
      summary: Get a list of items
      responses:
        '200':
          description: A list of items
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Item'

components:
  schemas:
    Item:
      type: object
      properties:
        id:
          type: integer
          format: int64
          example: 1
        name:
          type: string
          example: "Sample Item"
        status:
          type: string
          enum: []

2. Run command validate openapi-generator-cli validate test.yaml
3. It didn't show error about empty enum
4. It should be show error like this

Expected behavior

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Screenshots

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Operation System (please complete the following information):

• OS: [e.g. Ubuntu ]
• Version [e.g. 22]

Package System (please complete the following information):

• Version [e.g. 22]

Additional context

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