ASP.Net Update Panel

I'm getting a exception when my code runs. below is the error to my problem.

System.NullReferenceException was unhandled by user code
  Message=Object reference not set to an instance of an object.
  Source=App_Web_31dpeqc2
  StackTrace:
       at Customers.Page_Load(Object sender, EventArgs e) in f:\Aj's Documents\CPDM\IT-5284 ASP.NET\ASP Website\Customers.aspx.cs:line 38
       at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
       at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
       at System.Web.UI.Control.OnLoad(EventArgs e)
       at System.Web.UI.Control.LoadRecursive()
       at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
  InnerException: 

Below is the page that generated that error. The error comes when the page loads. The exception error occurs in under the page_load at the lvCustomers.DataSource = dt;

Before putting the updatepanel everything worked correctly now I'm getting this error. What I want the page to do is update only the data table when something is put into the txtSearch box onClick of the Search button.

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.Configuration;
using System.Data;

public partial class Customers : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
      //Create and open connection to database
        SqlConnection Conn = new SqlConnection(ConfigurationManager.ConnectionStrings["MyDatabase"].ConnectionString);

        Conn.Open();

        //Query to pick the data
        string sql = "SELECT LastName + ', ' + FirstName AS 'Customer Name',Email,City,State,Phone, CustomerID FROM Customer ORDER BY LastName, FirstName";

        //Sql Adapter
        SqlDataAdapter da = new SqlDataAdapter(sql, Conn);
            
        //Declare a data table
        DataTable dt = new DataTable();
    
        //Populate the data table
        da.Fill(dt);
    
        //Bind the listview   -->>Error is occuring here onload<<--
        lvCustomers.DataSource = dt;
        lvCustomers.DataBind();

        dt.Dispose();
        Conn.Close();
        da.Dispose();

    }
    protected void btnAddNewCustomer_Click(object sender, EventArgs e)
    {
        Response.Redirect("CustomerEdit.aspx?Mode=New");
    }
    protected void btnSearch_Click(object sender, EventArgs e)
    {

        string stext = txtSearch.Text;

        //Declare server connection
        SqlConnection Conn = new SqlConnection(ConfigurationManager.ConnectionStrings["MyDatabase"].ConnectionString);

        //Open Database
        Conn.Open();

        //Define the lookup query
        string sql = "SELECT * FROM CUSTOMER WHERE FirstName LIKE '%@stext%' OR LastName LIKE '%@stext%' OR City LIKE '%@stext%' OR State LIKE '%@stext%'";

        //Declare the command
        SqlCommand cmd = new SqlCommand(sql, Conn);

        //Add the parameters needed for the SQL Query
        cmd.Parameters.AddWithValue("@stext", stext);

        //Sql Adapter
        SqlDataAdapter da = new SqlDataAdapter();

        //Declare a data table
        DataTable dt = new DataTable();
        da.SelectCommand = cmd;

      
        //Populate the data table
        da.Fill(dt);

        lblConnectionResults.Text = sql;

        //Bind the listview
        lvCustomers.DataSource = dt;
        lvCustomers.DataBind();

        dt.Dispose();
        Conn.Close();
        da.Dispose();
        



    }
}

You are missing ContentTemplate tag inside of Update Panel

It should be like this.

<asp:UpdatePanel>
 <ContentTemplate></ContentTemplate>
 </asp:UpdatePanel>

Thanks,
Lijo