在将Excel文件上载到数据库时，不将对象引用设置为对象的实例

Question

请帮助。我在尝试将excel文件上传到数据库时收到此错误。错误发生在这行代码中：

SqlConnection MyCon = new SqlConnection(ConfigurationManager.ConnectionStrings[Excel107ConString].ConnectionString);

以下是我的全部代码。

public partial class WebForm1 : System.Web.UI.Page
    {
        string Excel107ConString = string.Empty;

        protected void Upload(object sender, EventArgs e)
        {

            string excelPath = Server.MapPath("~/Files/") + Path.GetFileName(FileUpload1.PostedFile.FileName);
            FileUpload1.SaveAs(excelPath);

            string conString = string.Empty;
            string extension = Path.GetExtension(FileUpload1.PostedFile.FileName);
            switch (extension)
            {

                case ".xls":
                    SqlConnection MyCon = new SqlConnection(ConfigurationManager.ConnectionStrings[Excel107ConString].ConnectionString);
                   break;

            }
            conString = string.Format(conString, excelPath);
            using (OleDbConnection excel_con = new OleDbConnection(conString))
            {

                excel_con.Open();
                string sheet1 = excel_con.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null).Rows[0]["TABLE_NAME"].ToString();
                DataTable dtExcelData = new DataTable();


                dtExcelData.Columns.AddRange(new DataColumn[3] { new DataColumn("InvoiceNumber", typeof(string)),
            new DataColumn("AmountPaid", typeof(decimal)),
            new DataColumn("Remarks",typeof(string)) });

                using (OleDbDataAdapter oda = new OleDbDataAdapter("SELECT * FROM [" + sheet1 + "]", excel_con))
                {
                    oda.Fill(dtExcelData);
                }
                excel_con.Close();

                string consString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
                using (SqlConnection con = new SqlConnection(consString))
                {
                    using (SqlBulkCopy sqlBulkCopy = new SqlBulkCopy(con))
                    {

                        sqlBulkCopy.DestinationTableName = "smarttable";


                        sqlBulkCopy.ColumnMappings.Add("InvoiceNumber", "InvoiceNumber");
                        sqlBulkCopy.ColumnMappings.Add("AmountPaid", "AmountPaid");
                        sqlBulkCopy.ColumnMappings.Add("Remarks", "Remarks");
                        con.Open();
                        sqlBulkCopy.WriteToServer(dtExcelData);
                        con.Close();
                    }
                }
            }
        }


}

请帮忙。