java.lang.NullPointerException: The obj parameter cannot be null
   at org.openide.util.Parameters.notNull(Parameters.java:89)
   at org.openide.nodes.Children$Dupl.updateListAndMap(Children.java:1728)
   at org.openide.nodes.Children$Dupl.updateList(Children.java:1704)
   at org.openide.nodes.Children$Keys.setKeys(Children.java:1503)
   at org.netbeans.modules.web.clientproject.node.ImportantFilesNodeFactory$ImportantFilesChildren.access$500(ImportantFilesNodeFactory.java:336)
   at org.netbeans.modules.web.clientproject.node.ImportantFilesNodeFactory$ImportantFilesChildren$2.run(ImportantFilesNodeFactory.java:481)
Caused: org.openide.util.RequestProcessor$SlowItem: task failed due to: java.lang.NullPointerException: The obj parameter cannot be null
   at org.openide.util.RequestProcessor.post(RequestProcessor.java:419)
   at org.netbeans.modules.web.clientproject.node.ImportantFilesNodeFactory$ImportantFilesChildren.refreshKeys(ImportantFilesNodeFactory.java:479)
   at org.netbeans.modules.web.clientproject.node.ImportantFilesNodeFactory$ImpFilesNL$Listener.propertyChange(ImportantFilesNodeFactory.java:183)
   at org.openide.util.WeakListenerImpl$PropertyChange.propertyChange(WeakListenerImpl.java:197)
   at java.beans.PropertyChangeSupport.fire(PropertyChangeSupport.java:335)
   at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:327)
   at org.netbeans.spi.project.support.ant.SequentialPropertyEvaluator.stateChanged(SequentialPropertyEvaluator.java:208)
   at org.openide.util.WeakListenerImpl$Change.stateChanged(WeakListenerImpl.java:330)
   at org.openide.util.ChangeSupport.fireChange(ChangeSupport.java:133)
   at org.openide.util.ChangeSupport.fireChange(ChangeSupport.java:119)
   at org.netbeans.spi.project.support.ant.ProjectProperties$PP$2.run(ProjectProperties.java:389)
   at org.netbeans.spi.project.support.ant.ProjectProperties$PP$2.run(ProjectProperties.java:387)
   at org.openide.util.Mutex.readAccess(Mutex.java:295)
   at org.netbeans.spi.project.support.ant.ProjectProperties$PP.fireChange(ProjectProperties.java:395)
   at org.netbeans.spi.project.support.ant.ProjectProperties$PP.put(ProjectProperties.java:253)
   at org.netbeans.spi.project.support.ant.ProjectProperties.putProperties(ProjectProperties.java:135)
   at org.netbeans.spi.project.support.ant.AntProjectHelper$6.run(AntProjectHelper.java:763)
   at org.netbeans.spi.project.support.ant.AntProjectHelper$6.run(AntProjectHelper.java:761)
   at org.openide.util.Mutex.writeAccess(Mutex.java:404)
   at org.netbeans.spi.project.support.ant.AntProjectHelper.putProperties(AntProjectHelper.java:761)
   at org.netbeans.modules.web.clientproject.ui.customizer.ClientSideProjectProperties.saveProperties(ClientSideProjectProperties.java:208)
   at org.netbeans.modules.web.clientproject.ui.customizer.ClientSideProjectProperties$2.run(ClientSideProjectProperties.java:149)
   at org.netbeans.modules.web.clientproject.ui.customizer.ClientSideProjectProperties$2.run(ClientSideProjectProperties.java:146)
   at org.openide.util.Mutex.writeAccess(Mutex.java:443)
   at org.netbeans.modules.web.clientproject.ui.customizer.ClientSideProjectProperties.save(ClientSideProjectProperties.java:146)
   at org.netbeans.modules.web.clientproject.ui.customizer.CustomizerProviderImpl$StoreListener.actionPerformed(CustomizerProviderImpl.java:151)
   at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2$1$1.run(CustomizerDialog.java:314)
   at org.openide.filesystems.FileUtil$2.run(FileUtil.java:447)
   at org.openide.filesystems.EventControl.runAtomicAction(EventControl.java:127)
   at org.openide.filesystems.FileSystem.runAtomicAction(FileSystem.java:609)
   at org.openide.filesystems.FileUtil.runAtomicAction(FileUtil.java:431)
   at org.openide.filesystems.FileUtil.runAtomicAction(FileUtil.java:451)
   at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2$1.run(CustomizerDialog.java:309)
   at org.openide.util.Mutex.writeAccess(Mutex.java:404)
   at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2.run(CustomizerDialog.java:306)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1423)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2033)