java.lang.IllegalArgumentException: view is invalid
        at javax.help.search.MergingSearchEngine.merge(MergingSearchEngine.java:94)
        at javax.help.JHelpSearchNavigator.merge(JHelpSearchNavigator.java:160)
        at javax.help.plaf.basic.BasicSearchNavigatorUI.addSubHelpSets(BasicSearchNavigatorUI.java:265)
        at javax.help.plaf.basic.BasicSearchNavigatorUI.reloadData(BasicSearchNavigatorUI.java:215)
        at javax.help.plaf.basic.BasicSearchNavigatorUI.installUI(BasicSearchNavigatorUI.java:164)
        at javax.swing.JComponent.setUI(JComponent.java:673)
        at javax.help.JHelpNavigator.setUI(JHelpNavigator.java:249)
        at javax.help.JHelpNavigator.updateUI(JHelpNavigator.java:268)
        at javax.help.JHelpNavigator.<init>(JHelpNavigator.java:97)
        at javax.help.JHelpSearchNavigator.<init>(JHelpSearchNavigator.java:58)
        at javax.help.SearchView.createNavigator(SearchView.java:72)
        at javax.help.JHelp.setupNavigators(JHelp.java:140)
        at javax.help.JHelp.<init>(JHelp.java:118)
        at javax.help.JHelp.<init>(JHelp.java:68)
        at org.netbeans.modules.javahelp.JavaHelp.createJHelp(JavaHelp.java:846)
        at org.netbeans.modules.javahelp.JavaHelp.showHelp(JavaHelp.java:426)
        at org.netbeans.api.javahelp.Help.showHelp(Help.java:72)
        at org.netbeans.modules.javahelp.HelpAction.actionPerformed(HelpAction.java:167)
        at org.openide.windows.TopComponent.processKeyBinding(TopComponent.java:971)
        at javax.swing.JComponent.processKeyBindings(JComponent.java:2895)
        at javax.swing.JComponent.processKeyEvent(JComponent.java:2812)
        at java.awt.Component.processEvent(Component.java:5877)
        at java.awt.Container.processEvent(Container.java:2058)
        at java.awt.Component.dispatchEventImpl(Component.java:4472)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Component.dispatchEvent(Component.java:4302)
        at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1848)
        at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:697)
        at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:962)
        at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:834)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:661)
        at java.awt.Component.dispatchEventImpl(Component.java:4344)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Window.dispatchEventImpl(Window.java:2440)
        at java.awt.Component.dispatchEvent(Component.java:4302)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at org.netbeans.core.TimeableEventQueue.dispatchEvent(TimeableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)