[BUG] kotlin-spring will generate array of enum to only enum object when field is marked required

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 we are trying to generate a List of Enums as one of our object's field, we found that it will only generate it as Enum itself, interesting part is if I remove the field from required, it will be wrapped by List but with ?.

All works well for spring, so it should be a bug of kotlin-spring.

openapi-generator version

bug exists in latest as well (6.0.0)

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: Test
  description: test
  version: '1.0.0'
servers:
  - url: http://localhost/v1/test
paths:
  /test:
    get:
      parameters:
        - name: "id"
          in: query
          description: id
          required: true
          schema:
            type: integer
            format: int64
      responses:
        200:
          description: reponse
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Response'

components:
  schemas:
    Response:
      type: object
      properties:
        flags:
          type: array
          items:
            type: string
            enum:
              - Value1
              - Value2
      required:
        - flags

Generation Details

/**
 * 
 * @param flags 
 */
data class Response(

        @field:NotNull 
        @JsonProperty("flags") val flags: Response.Flags
) {

    /**
    * 
    * Values: vaule1,vaule2
    */
    enum class Flags(val value: kotlin.String) {

        @JsonProperty("Vaule1") vaule1("Vaule1"),
        @JsonProperty("Vaule2") vaule2("Vaule2")
    }

}

Steps to reproduce

just generate

Suggest a fix

spring doesn't have this issue (java)

Start by running the kotlin-spring generator with the OpenAPI declaration in the issue, comparing the required and optional flags cases with the spring output. Trace the kotlin-spring generation entry point and verify that the required array-of-enum field is generated as a non-null list rather than a single enum; the generated Response model should match the schema.