ASP.Net Error: Session state is not available in this context

 Please help i would want to use the code below for my application to automatically be redirecting on all my web pages so that if the session expires it will always redirect to the login.

An exception of type 'System.Web.HttpException' occurred in System.Web.dll but was not handled in user code

Additional information: Session state is not available in this context.

Imports System.Web.Optimization

Public Class Global_asax
    Inherits HttpApplication

    Sub Application_Start(sender As Object, e As EventArgs)
        ' Fires when the application is started
        RouteConfig.RegisterRoutes(RouteTable.Routes)
        BundleConfig.RegisterBundles(BundleTable.Bundles)

        ' Code that runs when a new session is started
        If Session("Username") IsNot Nothing Then
            'Redirect to Welcome Page if Session is not null

            Response.Redirect("MenuAcademics.aspx")
        Else
            'Redirect to Login Page if Session is null & Expires 

            Response.Redirect("Logindata.aspx")
        End If
    End Sub
End Class

error comes here

   If Session("Username") IsNot Nothing Then