RedirectToAction TempData is NULL

Question

I am using TempData for storing ViewModel that is needed on a in the Register method.

My code snippet for RedirectToAction - shows adding ViewModel to TempData

           TempData.Put("Email", verificationResponse.Email);
           TempData.Put("Phone",verificationResponse.Phone);
            RegisterViewModel rvm = new RegisterViewModel
            {
                PolicyID = vm.PolicyID,
                FirstName = vm.FirstName,
                LastName = vm.LastName,
                DOBMM = vm.DOBMM,
                DOBDD = vm.DOBDD,
                DOBYYYY = vm.DOBYYYY,
                ZipCode = vm.ZipCode,
                ReturnUrl = vm.ReturnUrl,
                EnableRegister = true,
                Email = verificationResponse.Email, 
                Username = verificationResponse.Email

            };
            TempData.Put("rvm", rvm);
           
            return RedirectToAction("Register", "Auth");

But when I accessed TempData in Register it was null.

[HttpGet]
    public IActionResult Register()
    {
        RegisterViewModel rvm = TempData.Get<RegisterViewModel>("rvm");
        TempData.Keep("rvm");
        return View(rvm);
    }

Answer 1

Ensure that you do not store empty strings in TempData!!! You might think it's only a problem for one key/value pair. It's not! The entire TempData is null.

My problem was this line TempData.Put("Email", verificationResponse.Email); The verificationResponse.Email was an empty string and it caused the TempData to be null in the Register method.

Spent too much time looking at this bug.