hidden field value empty

Question

how to solve on first time page load (redirect one page to second page) hidden field value empty.

 

 Note:-

 

protected void imgbtncheckout_Click(object sender, EventArgs e)
{
try
{

double checkamount = 250.0;

double codeBehindValue = Convert.ToDouble(HDNshoppingamt.Value); // debugging HDNshoppingamt value empty.
if (codeBehindValue >= checkamount)
{

if (Session["userid"] != null)
{ 

...