The ConnectionString property has not been initialized. error shows when i run

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C#

i prepared excel sheet and read that excel data in to the database.

code as follows;

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;


public partial class _Default : System.Web.UI.Page 
{
    SqlConnection conn = new SqlConnection("Server=(local);Initial Catalog=master;Integrated Security=True  ");
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnUpload_Click(object sender, EventArgs e)
    {


        if ((txtFilePath.HasFile))
        {

            SqlConnection conn = new SqlConnection();
            SqlCommand cmd = new SqlCommand();
            SqlDataAdapter da = new SqlDataAdapter();
            DataSet ds = new DataSet();
            String query = null;
            string connString = "";
            string strFileName = DateTime.Now.ToString("ddMMyyyy_HHmmSS");
         string strFileType = System.IO.Path.GetExtension(txtFilePath.FileName).ToString().ToLower();


         
string strNewPath = Server.MapPath("~UploadedExcel/" + strFileName + strFileType);



            //Connection String to Excel Workbook

            if (strFileType.Trim() == ".xls")
            {

                connString = "Server=(local);Initial Catalog=master;Integrated Security=True" + strNewPath + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=2\"";

            }

            else if (strFileType.Trim() == ".xlsx")
            {
                connString = "Server=(local);Initial Catalog=master;Integrated Security=True" + strNewPath + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=2\"";
            }

            query = "select * from  StaffDetails";

            if (conn.State == ConnectionState.Closed) conn.Open();

            cmd = new SqlCommand(query, conn);
            da = new SqlDataAdapter(cmd);
            ds = new DataSet();
            da.Fill(ds);

            grvExcelData.DataSource = ds.Tables[0];
            grvExcelData.DataBind();

            lblMessage.Text = " data retrieved successfully! TOtal Records:" + ds.Tables[0].Rows.Count;
            lblMessage.ForeColor = System.Drawing.Color.Green;
            lblMessage.Visible = true;

            da.Dispose();
            conn.Close();
            conn.Dispose();
        }

        else
        {
            lblMessage.Text = "Please select an excel file first";
            lblMessage.ForeColor = System.Drawing.Color.Red;
            lblMessage.Visible = true;
        }
    }
}

when i run error shows;

The ConnectionString property has not been initialized.

in the conncetionstring line what is the error.please help line.

i think in the following line error;

connString = "Server=(local);Initial Catalog=master;Integrated Security=True" + strNewPath + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=2\"";

please help me.