[BUG] [C++] [Restbed] Restbed C++ OpenAPI Generator does not convert a vector of custom objects into a json string in the generated code

Description

Hi, I am using OpenAPI generator to generate Restbed C++ API server. Here is what I've noticed in the generated GET handler: for some reason resultObject never gets parsed, and the result is empty. Here is this handler from examples in the OpenAPI Generator repository:

void PetApiPetFindByStatusResource::handler_GET_internal(const std::shared_ptr<restbed::Session> session)
{
const auto request = session->get_request();

// Getting the query params

int status_code = 500;
std::vector<std::shared_ptr<Pet>> resultObject = std::vector<std::shared_ptr<Pet>>();
std::string result = "";

try {
    std::tie(status_code, resultObject) =
         handler_GET(status);
}
catch(const PetApiException& e) {
    std::tie(status_code, result) = handlePetApiException(e);
}
catch(const std::exception& e) {
    std::tie(status_code, result) = handleStdException(e);
}
catch(...) {
    std::tie(status_code, result) = handleUnspecifiedException();
}

if (status_code == 200) {

    const constexpr auto contentType = "application/json";
    //I want to return the result here but it would never happen since we are not using resultObject anywhere 
    returnResponse(session, 200, result.empty() ? "successful operation" : result, contentType);
    return;
}
if (status_code == 400) {

    const constexpr auto contentType = "text/plain";
    returnResponse(session, 400, result.empty() ? "Invalid status value" : result, contentType);
    return;
}
defaultSessionClose(session, status_code, result);
}

I can observe the same results for my project while using Restbed generator. I think the only way to fix it is to add some sort of result = resultObject.to_json_string() every time API is re-generated but this is not how it should work. Is there any workaround?

openapi-generator version

I am using version 5.4.0 which is the stable latest version.

OpenAPI declaration file content or url

Here is my .json spec file from my project that seems to be correct:

{
  "openapi": "3.0.0",
  "info": {
    "version": "1.0.0",
    "title": "My API"
  },
  "paths": {
    "/myobject": {
      "get": {
        "responses": {
          "200": {
            "content": {
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/MyObject"
                  }
                }
              }
            }
          },
          "default": {
            "description": "unexpected error"
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "MyObject": {
        "type": "object",
        "properties": {
          "prop1": {
            "type": "string"
          },
          "prop2": {
            "type": "number"
          }
        }
      }
    }
  }
}

Generation Details, Steps to Reproduce

I am using npx CLI tool to generate API using this command
npx @openapitools/openapi-generator-cli generate -i apispec.json -g cpp-restbed-server -o ../OpenAPI/generatedapi
The issue can be reproduced with help of Petstore example using Restbed generator, both for .json or .yaml spec.
npx @openapitools/openapi-generator-cli generate -i petstore.yaml -g cpp-restbed-server -o /tmp/restbed-test

In other words it seems to be easily reproduced. Please let me know if I can provide you with any more details.

Start with the generated samples/server/petstore/cpp-restbed/api/PetApi.cpp handler shown in the issue, then reproduce it with the petstore.yaml generation command. Trace how the vector result is handled after handler_GET; done means a successful array response contains the generated JSON rather than an empty or fallback message.