Cell.Text property of grid is blank when allowsorting is set to true

if (cell.Text == "Login")
{
  cell.Text = "TUSHAR";
}

if (cell.Text == "Login")
{
  cell.Text = "TUSHAR";
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;
using System.Configuration;
namespace RNDWeb
{
    public partial class GridViewRND : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {           
            BindDataUsingDataSet();
        }
        public void BindDataUsingDataSet()
        {
            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["RNDLocal"].ConnectionString);
            SqlCommand cmd = new SqlCommand("select ID,Login from users where login like 'survey%'", con);
            SqlDataAdapter dad = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            dad.Fill(ds);
            GridView grd = new GridView();
            grd.RowDataBound += GridView_RowDataBound;
            placeholder.Controls.Add(grd);
           grd.AllowSorting = true;
grd.DataSource = ds;
            grd.DataBind();
        }
        public void GridView_RowDataBound(Object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowIndex == 0)
            {
                e.Row.Visible = false;
            }
            if (e.Row.RowType == DataControlRowType.Header)
            {
                foreach (TableCell cell in e.Row.Cells)
                {
 if (cell.Text == "Login")
                    {
                        cell.Text = "TUSHAR";
                    }
            }
        }
    }
}