public IActionResult Book(int?id) { try { //book id missing if (id == null) { return(RedirectToAction("Error", "Home")); } ViewData["productId"] = id; BookViewModel model = _bookLoader.LoadBookModel(id.Value); var cat = _catalogueService.GetCategory(model.Category.ParentId.Value); if (cat.isOK && !cat.isEmpty) { model.Category.Parent = cat.data; } if (model == null) { return(RedirectToAction("Error", "Home")); } //to be sure //Or handle it in view model.Reviews = model.Reviews == null ? new List <Review>() : model.Reviews; return(View(model)); } catch (Exception e) { return(AlzaError.ExceptionActionResult(e)); } }