For example, in text editor click on a warning marker at <servlet-class> in web.xml that references non-existent Java class; or in Problems view call Quick Fix on that marker.

java.lang.NullPointerException
at org.jboss.tools.common.ui.marker.ConfigureProblemSeverityResolutionGenerator.findJavaElement(ConfigureProblemSeverityResolutionGenerator.java:66)
at org.jboss.tools.common.ui.marker.ConfigureProblemSeverityResolutionGenerator.getResolutions(ConfigureProblemSeverityResolutionGenerator.java:48)
at org.eclipse.ui.internal.ide.registry.MarkerHelpRegistry.getResolutions(MarkerHelpRegistry.java:253)
at org.jboss.tools.common.text.xml.MarkerAnnotationInfo.getMarkerProposals(MarkerAnnotationInfo.java:57)
at org.jboss.tools.common.text.xml.MarkerAnnotationInfo.getCompletionProposals(MarkerAnnotationInfo.java:45)
at org.jboss.tools.common.text.xml.JBDSQuickAssistProcessor.computeQuickAssistProposals(JBDSQuickAssistProcessor.java:72)
at org.eclipse.jface.text.quickassist.QuickAssistAssistant$ContentAssistProcessor.computeCompletionProposals(QuickAssistAssistant.java:75)
at org.eclipse.jface.text.contentassist.ContentAssistant.computeCompletionProposals(ContentAssistant.java:1830)
at org.eclipse.jface.text.contentassist.CompletionProposalPopup.computeProposals(CompletionProposalPopup.java:556)
at org.eclipse.jface.text.contentassist.CompletionProposalPopup.access$16(CompletionProposalPopup.java:553)
at org.eclipse.jface.text.contentassist.CompletionProposalPopup$2.run(CompletionProposalPopup.java:488)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.jface.text.contentassist.CompletionProposalPopup.showProposals(CompletionProposalPopup.java:482)
at org.eclipse.jface.text.contentassist.ContentAssistant.showPossibleCompletions(ContentAssistant.java:1656)
at org.eclipse.jface.text.quickassist.QuickAssistAssistant.showPossibleQuickAssists(QuickAssistAssistant.java:128)
at org.eclipse.jface.text.source.SourceViewer.doOperation(SourceViewer.java:933)
at org.eclipse.jface.text.source.projection.ProjectionViewer.doOperation(ProjectionViewer.java:1534)
at org.eclipse.wst.sse.ui.internal.StructuredTextViewer.doOperation(StructuredTextViewer.java:613)
at org.jboss.tools.common.model.ui.actions.xpl.SelectAnnotationRulerAction.runWithEvent(SelectAnnotationRulerAction.java:57)
at org.jboss.tools.common.model.ui.actions.xpl.SelectAnnotationRulerAction.run(SelectAnnotationRulerAction.java:46)
at org.jboss.tools.common.model.ui.actions.SelectRulerAction.mouseUp(SelectRulerAction.java:34)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:219)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1258)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3588)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3209)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2696)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2660)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2494)
at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:674)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:667)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:123)
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:344)
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:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:622)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:577)
at org.eclipse.equinox.launcher.Main.run(Main.java:1410)
at org.eclipse.equinox.launcher.Main.main(Main.java:1386)