Show GridView Header using EmptyDataTemplate when no data is available using C# in ASP.Net

I tried doing almost everything but my Gridview is not showing column header at all. Please help me.

here is my code:

 aspx markup

                            <asp:GridView ID="gvStudents" CssClass="table table-responsive table-bordered table-condensed table-hover" GridLines="None"
                                runat="server" AutoGenerateColumns="false">
                                <Columns>
                                    <asp:TemplateField ShowHeader="true" HeaderText="STS Number">
                                        <ItemTemplate>
                                            <asp:Label ID="lblstsno" runat="server" Text='<%#Eval("STS Number") %>'></asp:Label>
                                        </ItemTemplate>
                                    </asp:TemplateField>
                                    <asp:TemplateField ShowHeader="true" HeaderText="Student Name">
                                        <ItemTemplate>
                                            <asp:Label ID="lblname" runat="server" Text='<%#Eval("Student Name") %>'></asp:Label>
                                        </ItemTemplate>
                                    </asp:TemplateField>
                                    <asp:TemplateField ShowHeader="true" HeaderText="Mobile Number">
                                        <ItemTemplate>
                                            <asp:Label ID="lblmobile" runat="server" Text='<%#Eval("Mobile Number") %>'></asp:Label>
                                        </ItemTemplate>
                                    </asp:TemplateField>
                                    <asp:TemplateField ShowHeader="true" HeaderText="Class Studying In">
                                        <ItemTemplate>
                                            <asp:Label ID="lblclass" runat="server" Text='<%#Eval("Class Studying In") %>'></asp:Label>
                                        </ItemTemplate>
                                    </asp:TemplateField>
                                    <asp:TemplateField ShowHeader="true" HeaderText="Division">
                                        <ItemTemplate>
                                            <asp:Label ID="lbldiv" runat="server" Text='<%#Eval("Division") %>'></asp:Label>
                                        </ItemTemplate>
                                    </asp:TemplateField>
                                    <asp:TemplateField ShowHeader="true" HeaderText="Attendence">
                                        <ItemTemplate>
                                            <div class="checkbox icheckbox_square-blue">
                                                <asp:CheckBox ID="chkAttendence" runat="server" />
                                            </div>
                                        </ItemTemplate>
                                    </asp:TemplateField>
                                </Columns>
                            </asp:GridView>

c# code behind

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;

public partial class studentattendance : System.Web.UI.Page
{
    GlobalAccess ga = new GlobalAccess();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            this.txtDate.Text = DateTime.Now.ToShortDateString();
            this.PopulateStudentDetails();
        }
    }
    private void PopulateStudentDetails()
    {
        try
        {
            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["stjosephconnect"].ConnectionString);
            SqlDataAdapter da = new SqlDataAdapter("SELECT stsno as 'STS Number', name as 'Student Name', mobileno as 'Mobile Number', "
                                                   +"class as 'Class Studying In', div as 'Division' FROM studentregistration", con);
            DataSet ds = new DataSet();
            da.Fill(ds);
            gvStudents.DataSource = ds.Tables[0];
            gvStudents.DataBind();
        }
        catch(Exception ex)
        {
            Response.Write("<script language='javascript'>alert('" + Server.HtmlEncode(ex.Message.ToString()) + "')</script>");
        }        
    }

    protected void SaveStudentAttendance(object sender, EventArgs e)
    {
        try
        {
            foreach (GridViewRow row in gvStudents.Rows)
            {
                if (row.RowType == DataControlRowType.DataRow)
                {
                    CheckBox chkAttendance = row.FindControl("chkAttendence") as CheckBox;
                    string attendanceStatus = chkAttendance.Checked ? "Present" : "Absent";
                    int rollNo = int.Parse((row.FindControl("lblstsno") as Label).Text.Trim());
                    string studentName = ((row.FindControl("lblname") as Label).Text.Trim());
                    string Mobile = ((row.FindControl("lblmobile") as Label).Text.Trim());
                    string Class = ((row.FindControl("lblclass") as Label).Text.Trim());
                    string Division = ((row.FindControl("lbldiv") as Label).Text.Trim());
                    string sttendenceDate = (this.txtDate.Text.Trim());
                    string constring = ConfigurationManager.ConnectionStrings["stjosephconnect"].ConnectionString;
                    using (SqlConnection con = new SqlConnection(constring))
                    {
                        string query = "INSERT INTO studentattendance VALUES(@attdate, @name, @mobile, @class, @div, @attendance, @remarks, @status, @rem)";
                        using (SqlCommand cmd = new SqlCommand(query, con))
                        {
                            con.Open();
                            cmd.Parameters.AddWithValue("@attdate", this.txtDate.Text.Trim());
                            cmd.Parameters.AddWithValue("@name", studentName);
                            cmd.Parameters.AddWithValue("@mobile", Mobile);
                            cmd.Parameters.AddWithValue("@class", Class);
                            cmd.Parameters.AddWithValue("@div", Division);
                            cmd.Parameters.AddWithValue("@attendance", attendanceStatus);
                            cmd.Parameters.AddWithValue("@remarks", "Testing Purposes Only!");
                            cmd.Parameters.AddWithValue("@status", "1");
                            cmd.Parameters.AddWithValue("@rem", "0");
                            int i = cmd.ExecuteNonQuery();
                            if (i > 0)
                            {
                                ScriptManager.RegisterStartupScript(this, this.GetType(), "alert", "alert('Data saved successfully, Thank-You!');", true);
                            }
                            else
                            {
                                ScriptManager.RegisterStartupScript(this, this.GetType(), "alert", "alert('There was some error in connection');", true);
                            }
                            con.Close();
                        }
                    }
                }
            }
        }
        catch (Exception ex)
        {
            Response.Write("<script language='javascript'>alert('" + Server.HtmlEncode(ex.Message.ToString()) + "')</script>");
        }
    }
}