Nullable properties not showing correctly on swagger API response schema

Question

My SwaggerUI schema info is not showing which properties are nullable on the response, I want to generate a more accurate specification, there is any way to achieve this?.

Packages:

Swagger-Net 8.4.19.1 on .NET Framework 4.7

config.EnableSwagger(c =>
                    {
                        c.PrettyPrint();
                        c.UseFullTypeNameInSchemaIds();
                        c.GroupActionsBy(groupByFolder);
                        //c.OperationFilter<AddRequiredHeaderParameter>();
                        c.RootUrl(req => req.RequestUri.GetLeftPart(UriPartial.Authority) +
                                         req.GetRequestContext().VirtualPathRoot.TrimEnd('/'));
                        c.SingleApiVersion("v1", "namespace.WebApi");
                        c.ApiKey("Authorization", "header", "Bearer dasdasdasdasd....(/authenticate first)");
                    })
                    .EnableSwaggerUi(c =>
                    {
                        c.EnableDiscoveryUrlSelector();
                        c.DocExpansion(DocExpansion.List);
                    }
                    );
            }

Example:

[HttpGet]
[SwaggerResponse(HttpStatusCode.OK, Type = typeof(GetApplicationStatusResult))]
[Route("clients/{clientId}/applications/status")]
public HttpResponseMessage GetApplicationStatus(string clientId)
{
    return Request.CreateOkResponse(MobileAppManager.GetApplicationStatus(clientId));
}

public class GetApplicationStatusResult
{
    public Guid? ApplicationId { get; set; }
    public int? Type { get; set; }
    public int? Status { get; set; }
    public int? NewApplicationRemainingDays { get; set; }
}

Missing info on which properties are nullable:

https://i.stack.imgur.com/MzxoC.png

I already tried using the System.Web.Http.Description.ResponseType attribute instead of SwaggerResponse, the result was the same.

The whole solution is on .NET framework 4.7, (not .NET Core). I can't update it to core without losing weeks to refactor every controller in the solution.