java.lang.IllegalArgumentException: Argument cannot be null
	at org.eclipse.swt.SWT.error(SWT.java:4422)
	at org.eclipse.swt.SWT.error(SWT.java:4356)
	at org.eclipse.swt.SWT.error(SWT.java:4327)
	at org.eclipse.swt.widgets.Widget.error(Widget.java:476)
	at org.eclipse.swt.widgets.Combo.add(Combo.java:134)
	at org.jboss.tools.jst.web.ui.internal.css.dialog.CSSClassDialog.addNewClass(CSSClassDialog.java:269)
	at org.jboss.tools.jst.web.ui.internal.css.dialog.CSSClassDialog$2.widgetSelected(CSSClassDialog.java:165)
	at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:248)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4423)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1388)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3771)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3391)
	at org.eclipse.jface.window.Window.runEventLoop(Window.java:827)
	at org.eclipse.jface.window.Window.open(Window.java:803)
	at org.jboss.tools.jst.web.ui.internal.css.dialog.OpenCSSDialogHandler.execute(OpenCSSDialogHandler.java:36)
	at org.eclipse.ui.internal.handlers.HandlerProxy.execute(HandlerProxy.java:290)
	at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:90)
	at sun.reflect.GeneratedMethodAccessor62.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:56)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:243)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:224)
	at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:132)
	at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:163)
	at org.eclipse.core.commands.Command.executeWithChecks(Command.java:499)
	at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:508)
	at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:222)
	at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.executeItem(HandledContributionItem.java:776)
	at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.handleWidgetSelection(HandledContributionItem.java:668)
	at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.access$6(HandledContributionItem.java:652)
	at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem$4.handleEvent(HandledContributionItem.java:584)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4423)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1388)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3771)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3391)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1122)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1006)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:146)
	at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:615)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:566)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:125)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:109)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:80)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:372)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:226)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:636)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:591)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1450)
	at org.eclipse.equinox.launcher.Main.main(Main.java:1426)