public CustomStatusCodesMiddleware(RequestDelegate next, CustomStatusCodesOptions options)
 {
     this.options = options;
     _next = next;
     if (options.ResponseGenerator == null)
     {
         throw new ArgumentNullException("options.ResponseGenerator");
     }
 }
 // Note you may need to disable friendly error pages in IE to see some of the 4xx and 5xx results
 public StatusCodePage(RequestDelegate next, CustomStatusCodesOptions statusCodeOptions)
 {
     this.next = next;
     this.statusCodeOptions = statusCodeOptions;
 }