✅ NullPointException in the Update/Post method, but not in the Get Method

[HttpGet]  
    public IActionResult EditListingJ(int? Id)      
    { 
        try  
        {
            var ListingDTO_DBTable = _context.ListingDTO_DBTable.Find(Id);  
            if (ListingDTO_DBTable != null)  
            {  
                ListingProjectsDTO dtoModelEdit = new ListingProjectsDTO()
                {
                    Id = ListingDTO_DBTable.Id,
                    ListingName = ListingDTO_DBTable.ListingName
                }; 
                Console.WriteLine($"Got it"); //The GET method is fine, it grabs the id 
                return Json(dtoModelEdit);  
            } 
            
            return Json(null);  
            
        }  
        catch (Exception ex)  
        {  
            
            return null;  
        }  
    }  
    
    [HttpPost]  
    public IActionResult EditListingJ(ListingProjectsDTO editedDtoModel)      
    {
        if (ModelState.IsValid)
        {
                 //NullPointException!! why does this line stay always null, I don't understand   
                 ListingProjectsDTO _listingProjectsDtoEdit = _listingProjectsDtoRepository.getListingProjectsDto(editedDtoModel.Id);
                 _listingProjectsDtoEdit.Id = editedDtoModel.Id;
                 _listingProjectsDtoEdit.ListingName = editedDtoModel.ListingName;
                _context.ListingDTO_DBTable.Update(_listingProjectsDto);              
                _context.SaveChanges();  
                return Json(_listingProjectsDto);  
            

        }
        return Json(null);
    }