NPE on getting the fields from a DataSourceProvider if using crosstabs

If you try to write you own JRDataSourceProvider you got a NPE Reports using Crosstabs.

From Jasper Report 3.7.1 there is a method ReportQueryDialog::jButton2ActionPerformed(java.awt.event.ActionEvent evt)

Inside that method net.sf.jasperreports.engine.JasperReport jr = new net.sf.jasperreports.engine.JasperReport(report,"",null,null,"");

ist called. And here is the JRExpressionCollector initialised with null!

this variable is used inside JRBaseObjectFactory::visitCrosstab(JRCrosstab crosstab)

here it is also null and the variable not checked to null.

Then you got the NPE