java.lang.NullPointerException
   at org.openide.nodes.Children$Keys.setKeys(Children.java:1487)
   at org.openide.nodes.AsynchChildren$1.add(AsynchChildren.java:187)
   at org.netbeans.modules.maven.nodes.ProjectFilesNode$ProjectFilesChildren.createKeys(ProjectFilesNode.java:178)
   at org.openide.nodes.AsynchChildren.run(AsynchChildren.java:205)
Caused: org.openide.util.RequestProcessor$SlowItem: task failed due to: java.lang.NullPointerException
   at org.openide.util.RequestProcessor$Task.schedule(RequestProcessor.java:1452)
   at org.openide.nodes.AsynchChildren.addNotify(AsynchChildren.java:89)
   at org.openide.nodes.Children.callAddNotify(Children.java:575)
   at org.openide.nodes.EntrySupport$Default.getArray(EntrySupport.java:770)
   at org.openide.nodes.EntrySupport$Default.getNodes(EntrySupport.java:217)
   at org.openide.nodes.EntrySupport$Default.getNodesCount(EntrySupport.java:232)
   at org.openide.nodes.Children.getNodesCount(Children.java:520)
   at org.openide.nodes.FilterNode$Children$DefaultSupport.callGetNodesCount(FilterNode.java:1661)
   at org.openide.nodes.FilterNode$Children.getNodesCount(FilterNode.java:1612)
   at org.openide.explorer.view.TreeView$6.run(TreeView.java:997)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1411)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1991)