public IActionResult Upsert(int?id)
 {
     BulkyBook.Models.CoverType cover = new BulkyBook.Models.CoverType(); //SOME ERROR with Single class initialization.
     if (id == null)
     {
         // Create
         return(View(cover));
     }
     // Update
     cover = _coverTypeRepository.GetById(id.GetValueOrDefault());
     if (cover == null)
     {
         // Incorrect ID
         return(NotFound());
     }
     return(View(cover));
 }