Session NULL in MVC widget

I have a controller called Authenticate Controller.

I have created a MVC widget using authnticate controller. The code has a session value stored in an object. I ran this locally it works fine. When i add as a widget and insert into a page / template it throws following error:

NullReferenceException: Object reference not set to an instance of an object.

CODE:

[ControllerToolboxItem(Name="Authenticate",Title="Authenticate",SectionName="MVCWidget")]
    public class AuthenticateController : Controller
   
        private Authentication oSessionAuthRequest;
     
        public Authentication SessionAuthRequest
       

            get
           
                if (oSessionAuthRequest == null)
               
                    oSessionAuthRequest =(Authentication)Session[Constants.SessionKey]; //Session is null.

//NullReferenceException: Object reference not set to an instance of an object.
               
                return oSessionAuthRequest;
           
            set
           
                Session[Constants.SessionKey] = value;
           
       

STACK TRACE FOR ERROR

[NullReferenceException: Object reference not set to an instance of an object.] System.ComponentModel.ReflectPropertyDescriptor.SetValue(Object component, Object value) +718 Telerik.Sitefinity.Mvc.ControllerActionInvoker.DeserializeControllerProperties(MvcProxyBase proxyControl) +2079 Telerik.Sitefinity.Mvc.ControllerActionInvoker.TryInvokeAction(MvcProxyBase proxyControl, String& output) +265 Telerik.Sitefinity.Mvc.Proxy.MvcControllerProxy.ExecuteController() +89 System.Web.UI.Control.PreRenderRecursiveInternal() +155 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Control.PreRenderRecursiveInternal() +240 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4090