I am getting error while submitting the form for dropdown list in MVC 5 Value cannot be null. Parameter name: items

Question

I have a project in which I have a dropdown list which is bound to database. It is populating the values and my dropdown shows the values as well, but when I am submitting the form an error like below occurs:

Value cannot be null.
Parameter name: items
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentNullException: Value cannot be null. Parameter name: items

I have bound the dropdown to the database but on post the controller is getting my class object which has a gender property. I check that my model object has the correct, selected value from the dropdown, but when it moves to the statement modelstate.isvalid it returns false.

public ActionResult Create(Registration registration)
{
    if (ModelState.IsValid)
    {
        registration.ConfirmPassword = EncryptionLibrary.EncryptText(registration.ConfirmPassword);
        registration.Password= EncryptionLibrary.EncryptText(registration.Password);
        registration.Created_Date = DateTime.Now;

        if (ModelState.IsValid)
        {
            db.Registration.Add(registration);
            db.SaveChanges();
            ViewBag.teacher = "Teacher account has been created Successfully";
            return RedirectToAction("Create");
        }

        TempData["Faculty"] = "";
        var result = _IRegistration.AddFaculty(registration);

        if (result > 0)
        {
            TempData["Success"] = "Faculty Added Successfully";
            ModelState.Clear();
            return RedirectToAction("Create");
        }
    }
    return View(registration);
}

Below is my razor syntax for the dropdown to bind the values from viewbag:

  @Html.DropDownListFor(model=>model.Gender, new SelectList(ViewBag.Gender, "Id", "Name"), "Please select", new { @id = "ddlFruits",@class="btn form-text" })

I want to save the gender dropdown value into the database although it is getting populated then why it is saying Value cannot be null.
Parameter name: items