How to handle Session in IHttpModule?

See more:

C#

ASP.NET

Please see below code

public class URLRewriter : IHttpModule {

public void Dispose() {

}
public void Init( HttpApplication context ) {
    context.BeginRequest += new EventHandler( context_BeginRequest );
}

void context_BeginRequest( object sender, EventArgs e ) {
            //code to make custom URL
    }
}

Here i am using IHttpModule for making custom URL redirection. But it showing error while setting session in destination page.

ERROR LINE Code : HttpContext.Current.Session[USERADMIN] == null

ERROR MEssage: "{System.NullReferenceException: Object reference not set to an instance of an object."

Please help me.
Thanks