install birt 2.6.0.v20100525 build in linux as5, create a chart and try to specify value y serires, when dragging column into value y serires, npe was thrown out.

exception:

java.lang.nullpointerexception
	at java.lang.string.<init>(string.java:433)
	at org.eclipse.birt.chart.ui.swt.simpletexttransfer.nativetojava(simpletexttransfer.java:125)
	at org.eclipse.birt.chart.ui.swt.datatextdroplistener.dragenter(datatextdroplistener.java:71)
	at org.eclipse.swt.dnd.dndlistener.handleevent(dndlistener.java:60)
	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.widget.sendevent(widget.java:1258)
	at org.eclipse.swt.widgets.widget.sendevent(widget.java:1243)
	at org.eclipse.swt.widgets.widget.notifylisteners(widget.java:1060)
	at org.eclipse.swt.dnd.droptarget.drag_motion(droptarget.java:472)
	at org.eclipse.swt.dnd.droptarget.drag_motion(droptarget.java:271)
	at org.eclipse.swt.internal.gtk.os._gtk_main_do_event(native method)
	at org.eclipse.swt.internal.gtk.os.gtk_main_do_event(os.java:8163)
	at org.eclipse.swt.widgets.display.eventproc(display.java:1239)
	at org.eclipse.swt.internal.gtk.os._g_main_context_iteration(native method)
	at org.eclipse.swt.internal.gtk.os.g_main_context_iteration(os.java:2224)
	at org.eclipse.swt.widgets.display.readanddispatch(display.java:3157)
	at org.eclipse.jface.window.window.runeventloop(window.java:825)
	at org.eclipse.jface.window.window.open(window.java:801)
	at org.eclipse.birt.core.ui.frameworks.taskwizard.wizardbase.open(wizardbase.java:87)
	at org.eclipse.birt.chart.ui.swt.wizard.chartwizard.open(chartwizard.java:237)
	at org.eclipse.birt.chart.reportitem.ui.chartreportitembuilderimpl.open(chartreportitembuilderimpl.java:279)
	at org.eclipse.birt.report.designer.internal.ui.processor.extenedelementprocessor.editelement(extenedelementprocessor.java:64)
	at org.eclipse.birt.report.designer.internal.ui.views.defaultnodeprovider.performinsert(defaultnodeprovider.java:748)
	at org.eclipse.birt.report.designer.internal.ui.views.defaultnodeprovider.performrequest(defaultnodeprovider.java:420)
	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.birt.report.designer.ui.views.elementadapterinvocationhandler.invoke(elementadapterinvocationhandler.java:89)
	at $proxy0.performrequest(unknown source)
	at org.eclipse.birt.report.designer.ui.actions.baseinsertmenuaction.insertelement(baseinsertmenuaction.java:193)
	at org.eclipse.birt.report.designer.ui.actions.baseinsertmenuaction.run(baseinsertmenuaction.java:271)
	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:2629)
	at org.eclipse.ui.internal.workbench.runui(workbench.java:2593)
	at org.eclipse.ui.internal.workbench.access$4(workbench.java:2427)
	at org.eclipse.ui.internal.workbench$7.run(workbench.java:670)
	at org.eclipse.core.databinding.observable.realm.runwithdefault(realm.java:332)
	at org.eclipse.ui.internal.workbench.createandrunworkbench(workbench.java:663)
	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. only apply drag enter check to windows system since linux and mac don¡¯t support it.
verified in 2.6.0.v20100525-1629