STEP: Create new project STEP: Create and open new CSS file within this project (File > New > Others > Css File) STEP: Open CSS Dialog (via context menu) STEP: Click on the button Add CSS Class STEP: Enter a name and click on the button OK ASSERT: CSS Class was created FAIL: There is an error in Error log (Unhandled event loop exception) Unhandled event loop exception java.lang.IllegalArgumentException: Argument cannot be null at org.eclipse.swt.SWT.error(SWT.java:4400) at org.eclipse.swt.SWT.error(SWT.java:4334) at org.eclipse.swt.SWT.error(SWT.java:4305) 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:4410) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1388) at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3760) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3381) 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.GeneratedMethodAccessor72.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) 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:851) at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.handleWidgetSelection(HandledContributionItem.java:743) at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem.access$7(HandledContributionItem.java:727) at org.eclipse.e4.ui.workbench.renderers.swt.HandledContributionItem$4.handleEvent(HandledContributionItem.java:662) at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84) at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4410) at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1388) at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3760) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3381) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1113) at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:997) at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:146) at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:613) at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332) at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:567) at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150) at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124) 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:616) 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)