Eclipse Neon Javadoc help does not work

Question

I have an issue with Eclipse Neon where the Javadoc has suddenly stopped working. Running Lubuntu OS, w Eclipse Neon.3, I get the following stacktrace in the the error log when I hit the F2 button: I have uninstalled the plugins I installed before it worked fine, pydev, xtext, ,xtend and JHipster plugin, still same issue.

org.eclipse.e4.core.di.InjectionException: org.eclipse.core.commands.ExecutionException: While executing the action, an exception occurred
    at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:65)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:282)
    at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:264)
    at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:132)
    at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:152)
    at org.eclipse.core.commands.Command.executeWithChecks(Command.java:494)
    at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:488)
    at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:210)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.executeCommand(KeyBindingDispatcher.java:286)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.press(KeyBindingDispatcher.java:507)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.processKeyEvent(KeyBindingDispatcher.java:558)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.filterKeySequenceBindings(KeyBindingDispatcher.java:378)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.access$0(KeyBindingDispatcher.java:324)
    at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher$KeyDownFilter.handleEvent(KeyBindingDispatcher.java:86)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1605)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1339)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1366)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1349)
    at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1378)
    at org.eclipse.swt.widgets.Widget.gtk_key_press_event(Widget.java:764)
    at org.eclipse.swt.widgets.Control.gtk_key_press_event(Control.java:3465)
    at org.eclipse.swt.widgets.Composite.gtk_key_press_event(Composite.java:801)
    at org.eclipse.swt.widgets.Widget.windowProc(Widget.java:2000)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:5827)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:5498)
    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:9545)
    at org.eclipse.swt.widgets.Display.eventProc(Display.java:1275)
    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:2495)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4149)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1121)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1022)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:150)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:693)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:610)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:138)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:673)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:610)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1519)
    at org.eclipse.equinox.launcher.Main.main(Main.java:1492)
Caused by: org.eclipse.core.commands.ExecutionException: While executing the action, an exception occurred
    at org.eclipse.jface.commands.ActionHandler.execute(ActionHandler.java:123)
    at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:90)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:55)
    ... 53 more
Caused by: java.lang.NullPointerException
    at org.eclipse.jdt.internal.ui.text.java.hover.JavadocHover.getStyleSheet(JavadocHover.java:943)
    at org.eclipse.jdt.internal.ui.text.java.hover.JavadocHover.getHoverInfo(JavadocHover.java:747)
    at org.eclipse.jdt.internal.ui.text.java.hover.JavadocHover.internalGetHoverInfo(JavadocHover.java:635)
    at org.eclipse.jdt.internal.ui.text.java.hover.JavadocHover.getHoverInfo2(JavadocHover.java:627)
    at org.eclipse.jdt.internal.ui.text.java.hover.BestMatchHover.getHoverInfo2(BestMatchHover.java:164)
    at org.eclipse.jdt.internal.ui.text.java.hover.JavaInformationProvider.getInformation2(JavaInformationProvider.java:71)
    at org.eclipse.jface.text.information.InformationPresenter.computeInformation(InformationPresenter.java:310)
    at org.eclipse.jface.text.AbstractInformationControlManager.doShowInformation(AbstractInformationControlManager.java:1144)
    at org.eclipse.jface.text.AbstractInformationControlManager.showInformation(AbstractInformationControlManager.java:1134)
    at org.eclipse.jface.text.source.SourceViewer.doOperation(SourceViewer.java:950)
    at org.eclipse.jface.text.source.projection.ProjectionViewer.doOperation(ProjectionViewer.java:1461)
    at org.eclipse.jdt.internal.ui.javaeditor.JavaSourceViewer.doOperation(JavaSourceViewer.java:196)
    at org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor$AdaptedSourceViewer.doOperation(CompilationUnitEditor.java:201)
    at org.eclipse.ui.texteditor.TextOperationAction$1.run(TextOperationAction.java:130)
    at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
    at org.eclipse.ui.texteditor.TextOperationAction.run(TextOperationAction.java:127)
    at org.eclipse.ui.texteditor.AbstractTextEditor$InformationDispatchAction.run(AbstractTextEditor.java:1816)
    at org.eclipse.jface.action.Action.runWithEvent(Action.java:473)
    at org.eclipse.jface.commands.ActionHandler.execute(ActionHandler.java:118)
    ... 59 more

Answer 1

Reeeeeally late reply but the problem was that the Linux window manager was using an invalid window configuration hence all popup windows in SWT(Eclipse GUI engine) was crashing. Changed theme in Linux to default and was fine.