description:
npe thrown out when click keyboard in cross tab cube builder dlg

build:
2.6.0.v20100504-0630

steps to reproduce:
1. new a data source and data set
2. new a cube
3. in the cross tab cube builder dlg, click outline dataset first then press keboard 'a'

actual result:
npe thrown out

expect result:
no error.

errorlog:
java.lang.nullpointerexception
at org.eclipse.birt.report.designer.data.ui.property.abstractpropertydialog.showpage(abstractpropertydialog.java:565)
at org.eclipse.birt.report.designer.data.ui.property.abstractpropertydialog.showselectionpage(abstractpropertydialog.java:472)
at org.eclipse.birt.report.designer.data.ui.property.abstractpropertydialog$2$1.run(abstractpropertydialog.java:430)
at org.eclipse.swt.custom.busyindicator.showwhile(busyindicator.java:70)
at org.eclipse.birt.report.designer.data.ui.property.abstractpropertydialog$2.selectionchanged(abstractpropertydialog.java:425)
at org.eclipse.jface.viewers.viewer$2.run(viewer.java:162)
at org.eclipse.core.runtime.saferunner.run(saferunner.java:42)
at org.eclipse.ui.internal.jfaceutil$1.run(jfaceutil.java:49)
at org.eclipse.jface.util.saferunnable.run(saferunnable.java:175)
at org.eclipse.jface.viewers.viewer.fireselectionchanged(viewer.java:160)
at org.eclipse.jface.viewers.structuredviewer.updateselection(structuredviewer.java:2162)
at org.eclipse.jface.viewers.structuredviewer.handleselect(structuredviewer.java:1190)
at org.eclipse.jface.viewers.structuredviewer$4.widgetselected(structuredviewer.java:1220)
at org.eclipse.jface.util.openstrategy.fireselectionevent(openstrategy.java:228)
at org.eclipse.jface.util.openstrategy.access$4(openstrategy.java:222)
at org.eclipse.jface.util.openstrategy$1.handleevent(openstrategy.java:389)
at org.eclipse.swt.widgets.eventtable.sendevent(eventtable.java:84)
at org.eclipse.swt.widgets.widget.sendevent(widget.java:1234)
at org.eclipse.swt.widgets.display.rundeferredevents(display.java:3540)
at org.eclipse.swt.widgets.display.readanddispatch(display.java:3159)
at org.eclipse.jface.window.window.runeventloop(window.java:825)
at org.eclipse.jface.window.window.open(window.java:801)
at org.eclipse.birt.report.designer.ui.dialogs.basedialog.open(basedialog.java:111)
at org.eclipse.birt.report.designer.ui.cubebuilder.action.newcubeaction.run(newcubeaction.java:112)
at org.eclipse.jface.action.action.runwithevent(action.java:498)
at org.eclipse.jface.action.actioncontributionitem.handlewidgetselection(actioncontributionitem.java:584)
at org.eclipse.jface.action.actioncontributionitem.access$2(actioncontributionitem.java:501)
at org.eclipse.jface.action.actioncontributionitem$5.handleevent(actioncontributionitem.java:411)
at org.eclipse.swt.widgets.eventtable.sendevent(eventtable.java:84)
at org.eclipse.swt.widgets.widget.sendevent(widget.java:1234)
at org.eclipse.swt.widgets.display.rundeferredevents(display.java:3540)
at org.eclipse.swt.widgets.display.readanddispatch(display.java:3159)
at org.eclipse.ui.internal.workbench.runeventloop(workbench.java:2601)
at org.eclipse.ui.internal.workbench.runui(workbench.java:2565)
at org.eclipse.ui.internal.workbench.access$4(workbench.java:2399)
at org.eclipse.ui.internal.workbench$7.run(workbench.java:669)
at org.eclipse.core.databinding.observable.realm.runwithdefault(realm.java:332)
at org.eclipse.ui.internal.workbench.createandrunworkbench(workbench.java:662)
at org.eclipse.ui.platformui.createandrunworkbench(platformui.java:149)
at org.eclipse.ui.internal.ide.application.ideapplication.start(ideapplication.java:115)
at org.eclipse.equinox.internal.app.eclipseapphandle.run(eclipseapphandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.eclipseapplauncher.runapplication(eclipseapplauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.eclipseapplauncher.start(eclipseapplauncher.java:79)
at org.eclipse.core.runtime.adaptor.eclipsestarter.run(eclipsestarter.java:369)
at org.eclipse.core.runtime.adaptor.eclipsestarter.run(eclipsestarter.java:179)
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:585)
at org.eclipse.equinox.launcher.main.invokeframework(main.java:619)
at org.eclipse.equinox.launcher.main.basicrun(main.java:574)
at org.eclipse.equinox.launcher.main.run(main.java:1407)
fixed it.

check the null point code.
verify the bug on 2.6.0.v20100511-0630