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:1021)
   at org.netbeans.modules.javahelp.JavaHelp.createAndDisplayJHelp(JavaHelp.java:554)
   at org.netbeans.modules.javahelp.JavaHelp.showHelp(JavaHelp.java:533)
   at org.netbeans.modules.javahelp.HelpCtxProcessor$ShortcutAction.actionPerformed(HelpCtxProcessor.java:173)
   at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
   at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
   at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
   at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
   at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
   at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:833)
   at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:877)
   at java.awt.Component.processMouseEvent(Component.java:6535)
   at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
   at java.awt.Component.processEvent(Component.java:6300)
   at java.awt.Container.processEvent(Container.java:2236)
   at java.awt.Component.dispatchEventImpl(Component.java:4891)
   at java.awt.Container.dispatchEventImpl(Container.java:2294)
   at java.awt.Component.dispatchEvent(Component.java:4713)
   at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4888)
   at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:4525)
   at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:4466)
   at java.awt.Container.dispatchEventImpl(Container.java:2280)
   at java.awt.Window.dispatchEventImpl(Window.java:2750)
   at java.awt.Component.dispatchEvent(Component.java:4713)
   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:76)
   at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
   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:76)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:159)
   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)