[BUG][JAVA][NATIVE][ASYNC] Java Client Native Async does not work with list

[AceHack]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• [4.3.1-SNAPSHOT] What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• [No Data] What's the actual output vs expected output?

Description

ListSubscriptionsResponse is always null when calling listSubscriptions

This should return the real value

openapi-generator version

4.3.1-SNAPSHOT (No regression this a bug on a new feature)

OpenAPI declaration file content or url

OpenAPI Spec
DataLake-Subscription-SwaggerDocumentation.json.zip

Command line used for generation

in build.gradle.kts

openApiGenerate {
    inputSpec.set("https://xxx.yyy.zzz")
    validateSpec.set(true)
    generatorName.set("java")
    engine.set("mustache")
    skipOverwrite.set(false)
    outputDir.set(openApiGeneratedDir)
    apiPackage.set("datalake.subscription.api")
    invokerPackage.set("datalake.subscription.invoker")
    modelPackage.set("datalake.subscription.model")
    generateApiTests.set(false)
    generateApiDocumentation.set(false)
    generateModelTests.set(false)
    generateModelDocumentation.set(false)
    configOptions.set(mapOf(
            "java8" to "true",
            "dateLibrary" to "java8",
            "library" to "native",
            "asyncNative" to "true",
            "serializationLibrary" to "jackson"
    ))

Steps to reproduce

call listSubscriptions after generation

The code that's generated just looks wrong, looks like it always returns null.

  public CompletableFuture<ListSubscriptionsResponse> listSubscriptions (String maxItems, String ownerId, String nextToken) throws ApiException {

    HttpRequest.Builder localVarRequestBuilder = HttpRequest.newBuilder();

    String localVarPath = "/";

    List<Pair> localVarQueryParams = new ArrayList<>();
    localVarQueryParams.addAll(ApiClient.parameterToPairs("max-items", maxItems));
    localVarQueryParams.addAll(ApiClient.parameterToPairs("owner-id", ownerId));
    localVarQueryParams.addAll(ApiClient.parameterToPairs("next-token", nextToken));

    if (!localVarQueryParams.isEmpty()) {
      StringJoiner queryJoiner = new StringJoiner("&");
      localVarQueryParams.forEach(p -> queryJoiner.add(p.getName() + '=' + p.getValue()));
      localVarRequestBuilder.uri(URI.create(memberVarBaseUri + localVarPath + '?' + queryJoiner.toString()));
    } else {
      localVarRequestBuilder.uri(URI.create(memberVarBaseUri + localVarPath));
    }

    localVarRequestBuilder.header("Accept", "application/json");

      localVarRequestBuilder.method("GET", HttpRequest.BodyPublishers.noBody());
      if (memberVarReadTimeout != null) {
        localVarRequestBuilder.timeout(memberVarReadTimeout);
      }
      if (memberVarInterceptor != null) {
        memberVarInterceptor.accept(localVarRequestBuilder);
      }
      return memberVarHttpClient.sendAsync(
              localVarRequestBuilder.build(),
              HttpResponse.BodyHandlers.ofString()).thenComposeAsync(localVarResponse -> {
          if (localVarResponse.statusCode()/ 100 != 2) {
              return CompletableFuture.failedFuture(new ApiException(localVarResponse.statusCode(),
                  "listSubscriptions call received non-success response",
                  localVarResponse.headers(),
                  localVarResponse.body())
              );
          } else {
              return CompletableFuture.completedFuture(
                      null
              );
          }
      });
  }

[AceHack]

This works fine with asyncNative: false by the way.

[AceHack]

@wing328 @UkonnRa @joerg-wille

[AceHack]

It seems the problem is here:

openapi-generator/modules/openapi-generator/src/main/resources/Java/libraries/native/api.mustache

Lines 184 to 189 in a58441c

	{{#returnValue}}
	memberVarObjectMapper.readValue(localVarResponse.body(), new TypeReference<{{{returnType}}}>() {})
	{{/returnValue}}
	{{^returnValue}}
	null
	{{/returnValue}}

Should be returnType instead of returnValue.

[laballab]

Submitted a PR to fix this:
#6168