Data Controls :: How To Pass Session ID In HyperlinkField GridView

here i am passing session id, to another page there capturing id to display some content. But i am getting error as "Object reference not set to an instance of an object." while capturing id in redirected page.

<asp:HyperLink ID="myHyperlink" Text='<%# Eval("PersonName") %>' NavigateUrl='<%# Eval("ImageId", "~/Display.aspx?")%>' runat="server"></asp:HyperLink>

I have doubt near navigate url field. captured the same in display.aspx as,

string strImageid = (string)Session["ImageId"].ToString();
        if (strImageid != null)
{
some.....
}