Return ModelState errors gracefully to an AJAX request

BaseController.cs

        protected ActionResult JsonFormResponse(JsonRequestBehavior jsonRequestBehaviour = JsonRequestBehavior.DenyGet)
        {
            if (ModelState.IsValid)
            {
                return new HttpStatusCodeResult(200);
            }

            var errorList = new List<JsonValidationError>();
            foreach (var key in ModelState.Keys)
            {
                ModelState modelState = null;
                if (ModelState.TryGetValue(key, out modelState))
                {
                    foreach (var error in modelState.Errors)
                    {
                        errorList.Add(new JsonValidationError()
                        {
                            Key = key,
                            Message = error.ErrorMessage
                        });
                    }
                }
            }

            var response = new JsonResponse()
            {
                Type = "Validation",
                Message = "",
                Errors = errorList
            };
            
            Response.StatusCode = 400;
            return Json(response, jsonRequestBehaviour);
        }

JsonResponse.cs

    public class JsonResponse
    {
        public string Type { get; set; }
        public string Message { get; set; }
        public IEnumerable<JsonValidationError> Errors { get; set; }

        public JsonResponse()
        {
            Errors = new List<JsonValidationError>();
        }
    }

JsonValidationError.cs

    public class JsonValidationError
    {
        public string Key { get; set; }
        public string Message { get; set; }
    }