java.lang.IllegalArgumentException: view is invalid
   at javax.help.search.MergingSearchEngine.merge(MergingSearchEngine.java:91)
   at javax.help.JHelpSearchNavigator.merge(JHelpSearchNavigator.java:168)
   at javax.help.plaf.basic.BasicSearchNavigatorUI.addSubHelpSets(BasicSearchNavigatorUI.java:275)
   at javax.help.plaf.basic.BasicSearchNavigatorUI.reloadData(BasicSearchNavigatorUI.java:225)
   at javax.help.plaf.basic.BasicSearchNavigatorUI.installUI(BasicSearchNavigatorUI.java:174)
   at javax.swing.JComponent.setUI(JComponent.java:666)
   at javax.help.JHelpNavigator.setUI(JHelpNavigator.java:257)
   at javax.help.JHelpNavigator.updateUI(JHelpNavigator.java:276)
   at javax.help.JHelpNavigator.<init>(JHelpNavigator.java:105)
   at javax.help.JHelpSearchNavigator.<init>(JHelpSearchNavigator.java:66)
   at javax.help.SearchView.createNavigator(SearchView.java:80)
   at javax.help.JHelp.setupNavigators(JHelp.java:148)
   at javax.help.JHelp.<init>(JHelp.java:126)
   at javax.help.JHelp.<init>(JHelp.java:76)
   at org.netbeans.modules.javahelp.JavaHelp.createJHelp(JavaHelp.java:0)
   at org.netbeans.modules.javahelp.JavaHelp.createAndDisplayJHelp(JavaHelp.java:0)
   at org.netbeans.modules.javahelp.JavaHelp.showHelp(JavaHelp.java:0)
   at org.netbeans.api.javahelp.Help.showHelp(Help.java:0)
   at org.netbeans.modules.javahelp.HelpAction.actionPerformed(HelpAction.java:0)
   at org.netbeans.core.ModuleActions.invokeAction(ModuleActions.java:0)
   at org.netbeans.core.windows.ShortcutAndMenuKeyEventProcessor.processShortcut(ShortcutAndMenuKeyEventProcessor.java:0)
   at org.netbeans.core.windows.ShortcutAndMenuKeyEventProcessor.postProcessKeyEvent(ShortcutAndMenuKeyEventProcessor.java:0)
   at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:817)
   at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:1074)
   at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:945)
   at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:771)
   at java.awt.Component.dispatchEventImpl(Component.java:4760)
   at java.awt.Container.dispatchEventImpl(Container.java:2294)
   at java.awt.Window.dispatchEventImpl(Window.java:2746)
   at java.awt.Component.dispatchEvent(Component.java:4711)
   at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
   at java.awt.EventQueue.access$500(EventQueue.java:97)
   at java.awt.EventQueue$3.run(EventQueue.java:709)
   at java.awt.EventQueue$3.run(EventQueue.java:703)
   at java.security.AccessController.doPrivileged(AccessController.java:0)
   at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
   at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:90)
   at java.awt.EventQueue$4.run(EventQueue.java:731)
   at java.awt.EventQueue$4.run(EventQueue.java:729)
   at java.security.AccessController.doPrivileged(AccessController.java:0)
   at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:0)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:109)
   at java.awt.WaitDispatchSupport$2.run(WaitDispatchSupport.java:184)
   at java.awt.WaitDispatchSupport$4.run(WaitDispatchSupport.java:229)
   at java.awt.WaitDispatchSupport$4.run(WaitDispatchSupport.java:227)
   at java.security.AccessController.doPrivileged(AccessController.java:0)
   at java.awt.WaitDispatchSupport.enter(WaitDispatchSupport.java:227)
   at java.awt.Dialog.show(Dialog.java:1084)
   at org.netbeans.core.windows.services.NbPresenter.superShow(NbPresenter.java:0)
   at org.netbeans.core.windows.services.NbPresenter.doShow(NbPresenter.java:0)
   at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:0)
   at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:0)
   at org.netbeans.modules.openide.util.NbMutexEventProvider$Event.doEventAccess(NbMutexEventProvider.java:0)
   at org.netbeans.modules.openide.util.NbMutexEventProvider$Event.readAccess(NbMutexEventProvider.java:0)
   at org.netbeans.modules.openide.util.LazyMutexImplementation.readAccess(LazyMutexImplementation.java:0)
   at org.openide.util.Mutex.readAccess(Mutex.java:0)
   at org.netbeans.core.windows.services.NbPresenter.show(NbPresenter.java:0)
   at java.awt.Component.show(Component.java:1671)
   at java.awt.Component.setVisible(Component.java:1623)
   at java.awt.Window.setVisible(Window.java:1014)
   at java.awt.Dialog.setVisible(Dialog.java:1005)
   at org.netbeans.core.windows.services.DialogDisplayerImpl$1AWTQuery.showDialog(DialogDisplayerImpl.java:0)
   at org.netbeans.core.windows.services.DialogDisplayerImpl$1AWTQuery.run(DialogDisplayerImpl.java:0)
   at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
   at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
   at java.awt.EventQueue.access$500(EventQueue.java:97)
   at java.awt.EventQueue$3.run(EventQueue.java:709)
   at java.awt.EventQueue$3.run(EventQueue.java:703)
   at java.security.AccessController.doPrivileged(AccessController.java:0)
   at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:80)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:0)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)