Crystal Report - Sub report

I am trying to pass dataset to subreport in crystal report. Last line of this code gives error object reference error

if (string.IsNullOrEmpty(Convert.ToString(ds)) || ds.Tables[0].Rows.Count == 0)
                {
                    GlobalFormValidations.ShowInformationMsgBox("There Is No Report To Show...");
                    return;
                }

                var DocReport = new ReportDocument();
                var reportPath = Application.StartupPath + "\\Reports\\" + fileName + ".rpt";
                DocReport.Load(reportPath);
               
                DocReport.SetDataSource(ds);
                DocReport.OpenSubreport("rptBanquetBalanceReport.rpt").SetDataSource(ds.Tables[1]);