I am getting Object Null Reference error. I tried checking for null as done below but I am still getting the error.
List<Data> gvdta = (List<Data>)Session["Items"];
switch (this.dd_search.SelectedValue)
{
    case "emp":                
    var tb = (from ad in gvdta
              where ad!=null & ad.emp.ToLower().Contains(this.txt_Search.Text.ToLower())
              select ad);
       gvdta = tb.ToList();            
    break;
}
Is there any other way? Please help.Thank you.
 
    