Sometimes you get a
"null" dataset argument
Exception when building the "Early Morning Report".
It is not very easy to reproduce. Sometimes you can create the report without any problems but sometimes you get this exception.
Anyways I was able to find the cause for this.
It seems that JasperReports uses JFreeChart to draw the charts.
And they had a NP-Problem --> http://www.jfree.org/phpBB2/viewtopic.php?f=3&t=27265&sid=51501c9d3d7401b482c07282e117d153
It seems that there is a fix in version 1.0.13 of jfreechart.
However JasperReports uses JFreeChart 1.0.12, even in the latest JasperReports version (5.6.1).