[BUG][C++][Pistache-server] Array of string : The generator omits the "setter" and xxxIsSet()

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• 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?
• [Optional] Bounty to sponsor the fix (example)

Description

The generator does generates lots of usual code but the setter of the member variable (std::vectorstd::string type) is not here.

The getter is also "strange" or at least unsual because it returns the reference on the member without the qualification const, so that it may be modified.

Last, the usual function ClassName::memberNameIsSet() is not generated too.

On the opposite, lots of code is well generated and running, for example toJson and fromJson methods (except the the set of the bool variable m_xxxIsSet = true
unsetXXXX() is also well generated.

openapi-generator version

Current master 4.0.0-SNAPSHOT

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  version: 1.0.0
  title: Check generation of array of object (Pistache)
  description: Internal ref filename is check_array_of_strings.yaml

servers:
  - url: http://localhost:8080

paths:
  /stair1:
    post:
      summary: blabla
      operationId: check_generation
      tags:
        - Stair1
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/UeContext'
        required: true
      responses:
        '200':
          description: Expected response to a valid request
          content:
            application/json:
              schema:
                type: string
        default:
          description: Unexpected error

components:
  schemas:
    UeContext:
      type: object
      properties:
        groups:
          type: array
          items:
            $ref: '#/components/schemas/GroupId'
          minItems: 0

    ObjectId:
      type: object
      properties:
        events:
          $ref: '#/components/schemas/GroupId'

    GroupId:
      type: string

Command line used for generation

Generate :

openapi-generator-cli.sh generate -i ./openapi.yaml -g cpp-pistache-server -c ./config.json -o .

Compile :

g++ -c  -I./api -I./model -I./impl -Wall -g -std=c++11 -o obj/model/UeContext.o model/UeContext.cpp

Steps to reproduce

Generate & compile

Related issues/PRs

N/A

Suggest a fix

EDIT: See below in the comment please

Start by running the generation command with openapi.yaml and config.json, then inspect the generated model/UeContext.cpp and its header. Compare the generated members for the groups array with the existing getter, unsetter, toJson, and fromJson methods. Done means the setter and groupsIsSet() are generated consistently and the provided g++ compilation succeeds.