Not Getting Data Nullable Exception

Question

public ActionResult Logout(UserProfile objUser)

{

{

if (ModelState.IsValid)

{

using (SessionEntities Db = new SessionEntities())

{

var obj = Db.UserProfiles.Where(a => a.UserName.Equals(objUser.UserName) && a.Password.Equals(objUser.Password)).FirstOrDefault();

if (obj != null)

{

Session["UserName"] = objUser.UserName.ToString();

// Session["UserName"] = obj.UserName.ToString();

// Session.Remove(a.ToString());

Session.Abandon();

return RedirectToAction("Login");

}

else

{

return RedirectToAction("Admin");

}

}

}

}

return RedirectToAction("UserDashBoard");

}