Site Master on page load

I have a few hyper link on the content place holder on the Site Master and would like to check if user login then set visible to true, if not set to false.
code like following:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load       
 If Request.IsAuthenticated Then
        MyHyperLink.Visible = True
   Else
             MyHyperLink.Visible = False        
End If
The code works on Default.aspx, but it fails on Site.Master.
I got error message "Object Reference not set to an insatance of an object"
If I put in Default then I need to have them onall the forms. I have to have them on Site,Master since I can have them in one file.
I would like to know any work around to have them on the Site.M ...