Grid View in Asp.net c#

i want to update the row in gridview but it gives me one error Object reference not set to an instance of an object. i have product table.



protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        SqlConnection conn = new SqlConnection("Data Source=ABC-59236A7CB6F;Initial Catalog=practical2;Integrated Security=True");
        conn.Open();
       
       
        GridView1.EditIndex = e.NewEditIndex;
        DataSet ds = new DataSet();
        SqlDataAdapter da;
        DataTable dt = new DataTable();
        da = new SqlDataAdapter("select * from pr ...