line below with new JREmptyDataSource() will get pdf as per expected.
jasperPrint = JasperFillManager.fillReport(report, jrParam, new JREmptyDataSource());
vs
where as using static _DATA_SOURCE_EMPTY, will always get blank pdf.
private static JREmptyDataSource _DATA_SOURCE_EMPTY = new JREmptyDataSource();
...
jasperPrint = JasperFillManager.fillReport(report, jrParam, _DATA_SOURCE_EMPTY);
...