created an attachment (id=158409)
screen shot

description:
error occurs when switching to 'parameters' page in data set.

build id:
2.5.2 v20100208-0630

steps to reproduce:
1. new a data set with a query using parameter,like:
select *
from classicmodels.customers
where classicmodels.customers.customernumber = ?
2. new a report parameter.
3. open the data set and switch to parameters page.

actual result:
npe occurs. see attached screen shot.
error log:
java.lang.nullpointerexception
	at org.eclipse.birt.report.designer.data.ui.dataset.parameterpageutil.getscalarparameter(parameterpageutil.java:216)
	at org.eclipse.birt.report.designer.data.ui.dataset.datasetparameterspage.refreshlinkedreportparamstatus(datasetparameterspage.java:451)
	at org.eclipse.birt.report.designer.data.ui.dataset.datasetparameterspage.pageactivated(datasetparameterspage.java:592)
	at org.eclipse.birt.report.designer.data.ui.property.abstractpropertydialog.showpage(abstractpropertydialog.java:575)
	at org.eclipse.birt.report.designer.data.ui.property.abstractpropertydialog.showselectionpage(abstractpropertydialog.java:472)
	at org.eclipse.birt.report.designer.data.ui.dataset.dataseteditor.showselectionpage(dataseteditor.java:895)
	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.core.runtime.platform.run(platform.java:888)
	at org.eclipse.ui.internal.jfaceutil$1.run(jfaceutil.java:48)
	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:2132)
	at org.eclipse.jface.viewers.structuredviewer.handleselect(structuredviewer.java:1160)
	at org.eclipse.jface.viewers.structuredviewer$4.widgetselected(structuredviewer.java:1190)
	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:1003)
	at org.eclipse.swt.widgets.display.rundeferredevents(display.java:3910)
	at org.eclipse.swt.widgets.display.readanddispatch(display.java:3503)
	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:110)
	at org.eclipse.birt.report.designer.data.ui.providers.editabledatasetnodeprovider.performedit(editabledatasetnodeprovider.java:99)
	at org.eclipse.birt.report.designer.internal.ui.views.defaultnodeprovider.performrequest(defaultnodeprovider.java:432)
	at org.eclipse.birt.report.designer.internal.ui.views.actions.editaction.doaction(editaction.java:90)
	at org.eclipse.birt.report.designer.internal.ui.views.actions.abstractelementaction.run(abstractelementaction.java:70)
	at org.eclipse.birt.report.designer.internal.ui.views.renamelistener.doubleclick(renamelistener.java:214)
	at org.eclipse.jface.viewers.structuredviewer$1.run(structuredviewer.java:821)
	at org.eclipse.core.runtime.saferunner.run(saferunner.java:42)
	at org.eclipse.core.runtime.platform.run(platform.java:888)
	at org.eclipse.ui.internal.jfaceutil$1.run(jfaceutil.java:48)
	at org.eclipse.jface.util.saferunnable.run(saferunnable.java:175)
	at org.eclipse.jface.viewers.structuredviewer.firedoubleclick(structuredviewer.java:819)
	at org.eclipse.jface.viewers.abstracttreeviewer.handledoubleselect(abstracttreeviewer.java:1419)
	at org.eclipse.jface.viewers.structuredviewer$4.widgetdefaultselected(structuredviewer.java:1195)
	at org.eclipse.jface.util.openstrategy.firedefaultselectionevent(openstrategy.java:238)
	at org.eclipse.jface.util.openstrategy.access$0(openstrategy.java:235)
	at org.eclipse.jface.util.openstrategy$1.handleevent(openstrategy.java:296)
	at org.eclipse.swt.widgets.eventtable.sendevent(eventtable.java:84)
	at org.eclipse.swt.widgets.widget.sendevent(widget.java:1003)
	at org.eclipse.swt.widgets.display.rundeferredevents(display.java:3910)
	at org.eclipse.swt.widgets.display.readanddispatch(display.java:3503)
	at org.eclipse.ui.internal.workbench.runeventloop(workbench.java:2405)
	at org.eclipse.ui.internal.workbench.runui(workbench.java:2369)
	at org.eclipse.ui.internal.workbench.access$4(workbench.java:2221)
	at org.eclipse.ui.internal.workbench$5.run(workbench.java:500)
	at org.eclipse.core.databinding.observable.realm.runwithdefault(realm.java:332)
	at org.eclipse.ui.internal.workbench.createandrunworkbench(workbench.java:493)
	at org.eclipse.ui.platformui.createandrunworkbench(platformui.java:149)
	at org.eclipse.ui.internal.ide.application.ideapplication.start(ideapplication.java:113)
	at org.eclipse.equinox.internal.app.eclipseapphandle.run(eclipseapphandle.java:194)
	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:368)
	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:559)
	at org.eclipse.equinox.launcher.main.basicrun(main.java:514)
	at org.eclipse.equinox.launcher.main.run(main.java:1311)
fixed
verified in 2.5.2.v20100209