ผมทำการเรียกข้อมูลเพื่อแสดงใน CrystalReport แต่ว่าเกิดตอนป้อนข้อมูลค้นหาซ้ำดันบอกว่า"Object reference not set to an instance of an object."

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Configuration;
using System.Data.SqlClient;
using CrystalDecisions.CrystalReports.Engine;
using System.Diagnostics;
using System.IO;

namespace Disbursed
{
    public partial class ReportPrint : Form
    {
        //Variable Type or new object
        SqlConnection conn = new SqlConnection();
        DataSet ds = new DataSet();
        DataTable dt = null;
        SqlDataAdapter da = new SqlDataAdapter();
        SqlCommand cmd = new SqlCommand();

        public ReportPrint()
        {
            InitializeComponent();
        }

        private void ReportPrint_Load(object sender, EventArgs e)
        {

        }

        private void tsb_SearchReport_Click(object sender, EventArgs e)
        {
            //Connecting your database = App.config("AppName")
            ConnectionStringSettings conSettings = ConfigurationManager.ConnectionStrings["ApplicationDatabase"];
            string ConnectionStrings = conSettings.ConnectionString;
            conn = new SqlConnection(ConnectionStrings);
            conn.Open();
            if (tstb_ProjKey.Text != "")
            {
                string sql = null;
                sql = "SELECT * FROM CommiteeReq WHERE ProjKey =" + tstb_ProjKey.Text;
                SqlCommand cmd = new SqlCommand(sql, conn);
                ds.Clear();
                da.SelectCommand = cmd;     // บรรทัดนี้ครับที่มีปัญหา รบกวนใครรู้อธิบายหน่อยครับ
                da.Fill(ds, "CommiteeReqReport");
                dt = ds.Tables["CommiteeReqReport"];
                da = null;
                conn.Close();
                conn = null;
                ReportDocument ReportDis = new ReportDocument();
                string directory = AppDomain.CurrentDomain.BaseDirectory;
                ReportDis.Load(directory + "\\CrystalReportDis.rpt");
                //ReportDis.Load("D:\\Disbursed\\CrystalReportDis.rpt");
                ReportDis.SetDataSource(dt);
                this.crystalReportViewer1.ReportSource = ReportDis;
                this.crystalReportViewer1.Refresh();
            }
            else
            {
                MessageBox.Show("กรุณากรอกเลขโครงการเพื่อดูรายงานครับ");

            }
            

        }

    }
}