Radio Button List value is showing null when I am assigning in Gridview

Question

Error is showing

Object reference not set to an instance of an object.

at rdb5.SelectedValue = "1" and going to catch block. Data is coming right and going inside the loop but error is showing at rdb5.SelectedValue = "1".

RadioButtonList rdb5 = (RadioButtonList)e.Row.FindControl("rdb5");
RadioButtonList rdb6 = (RadioButtonList)e.Row.FindControl("rdb6");
RadioButtonList rdb7 = (RadioButtonList)e.Row.FindControl("rdb7");
using (SqlConnection con = new SqlConnection(ConfigurationSettings.AppSettings["ConStr1"]))
{

    string sql = "select * from RateSchedule ";
    SqlCommand cmd = new SqlCommand(sql, con);
    SqlDataAdapter adpt = new SqlDataAdapter(cmd);
    DataSet ds = new DataSet();
    adpt.Fill(ds);
    string s = ds.Tables[0].Rows[0]["RegularLabor"].ToString().Trim();

    if (ds.Tables[0].Rows[0]["TaskType"].ToString() == "Default")
    {

    }
    if (ds.Tables[0].Rows[0]["RegularLabor"].ToString().Trim() == "True")
    {
        rdb5.SelectedValue = "1";
        //Here it is showing error "Object reference not set to an instance of an object."
    }
    else
    {
        rdb5.SelectedValue = "2";
    }