Get RadioButtonList Selected Value in Footer Row of ASP.Net GridView

Dear All,

May  i know why i get an error ? Kindly advise. thank you

   <asp:RadioButtonList ID="rdoButton1" runat="server" RepeatDirection="Horizontal" RepeatLayout="Table">
                <asp:ListItem Text="Yes" Value="TRUE"></asp:ListItem>
                <asp:ListItem Text="No" Value="FALSE"></asp:ListItem>
            </asp:RadioButtonList>           

   bool Domain = ((RadioButtonList)gvITAsset.FooterRow.FindControl("rdoButton1")).Checked ? "TRUE" : "FALSE";