Reproducing Steps:

1. open zss.test\export.zul
2. click "generate and insert chart" button to insert charts
3. click "Export PDF" button

Actual:
popup a error message >> "24"

java.lang.ArrayIndexOutOfBoundsException: 24
at org.zkoss.zss.model.impl.pdf.PdfExporter.layoutCharts(PdfExporter.java:1023)
at org.zkoss.zss.model.impl.pdf.PdfExporter.access$16(PdfExporter.java:982)
at org.zkoss.zss.model.impl.pdf.PdfExporter$PdfHeaderFooter.onEndPage(PdfExporter.java:1612)
at com.lowagie.text.pdf.PdfDocument.newPage(Unknown Source)
at com.lowagie.text.Document.newPage(Unknown Source)
at org.zkoss.zss.model.impl.pdf.PdfExporter.printColumns(PdfExporter.java:580)
at org.zkoss.zss.model.impl.pdf.PdfExporter.exportSheet(PdfExporter.java:301)
at org.zkoss.zss.model.impl.pdf.PdfExporter.export(PdfExporter.java:181)
at org.zkoss.zss.api.impl.ExporterImpl.export(ExporterImpl.java:49)
at zss.testapp.ExportComposer.toPdf(ExportComposer.java:210)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.zkoss.zk.ui.select.Selectors$ComposerEventListener.onEvent(Selectors.java:681)
at org.zkoss.zk.ui.AbstractComponent.onEvent(AbstractComponent.java:2746)
at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:2717)
at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:2658)
at org.zkoss.zk.ui.impl.EventProcessor.process(EventProcessor.java:136)
at org.zkoss.zk.ui.impl.UiEngineImpl.processEvent(UiEngineImpl.java:1765)
at org.zkoss.zk.ui.impl.UiEngineImpl.process(UiEngineImpl.java:1550)
at org.zkoss.zk.ui.impl.UiEngineImpl.execUpdate(UiEngineImpl.java:1260)
at org.zkoss.zk.au.http.DHtmlUpdateServlet.process(DHtmlUpdateServlet.java:603)
at org.zkoss.zk.au.http.DHtmlUpdateServlet.doGet(DHtmlUpdateServlet.java:485)
at org.zkoss.zk.au.http.DHtmlUpdateServlet.doPost(DHtmlUpdateServlet.java:494)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:755)