[BUG] openapi-generator-cli generates C# code that ignores incorrect server responses

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

The deserialization logic which is output in clients throws an ApiException in case the deserialization fails:

try
{
    return JsonConvert.DeserializeObject(response.Content, type, _serializerSettings);
}
catch (Exception e)
{
    throw new ApiException(500, e.Message);
}

However RestSharp's ExecuteAsync (which is being used in ApiClient) catches it, and ApiClient continues with an IRestResponse whose Data field is null:

response = await client.ExecuteAsync<T>(req, cancellationToken).ConfigureAwait(false);

The response is then converted into an ApiResponse<T> where Data is null and ErrorText is set:

var result = ToApiResponse(response);
if (response.ErrorMessage != null)
{
    result.ErrorText = response.ErrorMessage;
}

Then, the generated Api class returns it (this.ExceptionFactory!=null is true, but this.ExceptionFactory("ListBatchComplianceJobs", localVarResponse); returns null):

var localVarResponse = await this.AsynchronousClient.GetAsync<MultiComplianceJobResponse>("/2/compliance/jobs", localVarRequestOptions, this.Configuration, cancellationToken).ConfigureAwait(false);

if (this.ExceptionFactory != null)
{
    Exception _exception = this.ExceptionFactory("ListBatchComplianceJobs", localVarResponse);
    if (_exception != null) throw _exception;
}

return localVarResponse;

Then the `null data field is returned:

Foo.Client.ApiResponse<MultiComplianceJobResponse> localVarResponse = await ListBatchComplianceJobsWithHttpInfoAsync(type, status, cancellationToken).ConfigureAwait(false);
return localVarResponse.Data;

openapi-generator version

5.3.1

OpenAPI declaration file content or url

https://api.twitter.com/2/openapi.json

Generation Details

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli generate \
    -i https://api.twitter.com/2/openapi.json \
    -g csharp-netcore \
    -o /local/out/C#

• some syntax error fixes

Steps to reproduce

• Generate source code
• Fix syntax errors introduced by #10897
• Execute a request that returns an invalid enum variant
• Observe that null is returned, instead of a thrown ApiException

Suggest a fix

I don't know your code base well enough to suggest a solution. Is it intended that the ExceptionFactory returns null?

Start with the generated C# ApiClient and API methods using the csharp-netcore generator command described in the issue. Reproduce with the Twitter OpenAPI document and a response containing an invalid enum variant, then trace how RestSharp, ToApiResponse, and ExceptionFactory handle the deserialization failure. Done means the invalid response produces the intended ApiException rather than returning null data.