[Solved] Session is null inside default Constructor of Controller in ASP.Net MVC

namespace WebApplication1.Controllers
{
    public class Normal_UserController : Controller
    {   
        public Normal_UserController()
        {            
            //var Username = (string)Session["User"];
            ViewBag.DOM_TreeViewMenu = PopulateMenuDataTable();
        }
        private SqlConnection conn;
        private SqlDataAdapter da;
        private DataTable dt;       

        public ActionResult Startup ()
        {          
            return View();
        }
        public ActionResult Index()
        {
            ViewBag.DOM_TreeViewMenu = PopulateMenuDataTable();

            return View();
        }

        public ActionResult test()
        {            
            return View();
        }
      
        public ActionResult test2()
        {
            return View();
        }

        public ActionResult test3()
        {
            return View();
        }

if i am uncommiting this it gives me object value not set an instance of an object 

//var Username = (string)Session["User"];

i am doing statup class i got the value but not getting the value in 

public Normal_UserController() {
    //var Username = (string)Session["User"]; ViewBag.DOM_TreeViewMenu = PopulateMenuDataTable();
}