java.lang.AssertionError
        at org.netbeans.modules.masterfs.filebasedfs.children.ChildrenSupport.addChild(ChildrenSupport.java:118)
        at org.netbeans.modules.masterfs.filebasedfs.children.ChildrenSupport.rescanChildren(ChildrenSupport.java:228)
        at org.netbeans.modules.masterfs.filebasedfs.children.ChildrenSupport.getChildren(ChildrenSupport.java:75)
        at org.netbeans.modules.masterfs.filebasedfs.fileobjects.FolderObj$FolderChildrenCache.getChildren(FolderObj.java:516)
        at org.netbeans.modules.masterfs.filebasedfs.fileobjects.FolderObj.getChildren(FolderObj.java:131)
        at org.openide.loaders.MultiFileLoader.checkFiles(MultiFileLoader.java:332)
        at org.openide.loaders.MultiDataObject.checkFiles(MultiDataObject.java:987)
        at org.openide.loaders.MultiDataObject.checkSecondary(MultiDataObject.java:169)
        at org.openide.loaders.MultiDataObject.synchObjectSecondary(MultiDataObject.java:223)
        at org.openide.loaders.FilesSet.doLazyWork(FilesSet.java:95)
        at org.openide.loaders.FilesSet.size(FilesSet.java:174)
        at org.openide.loaders.DataNode$LazyFilesSet.size(DataNode.java:1096)
        at org.netbeans.modules.java.source.tasklist.ErrorAnnotator.annotateIcon(ErrorAnnotator.java:111)
        at org.netbeans.modules.masterfs.filebasedfs.FileBasedFileSystem$StatusImpl.annotateIcon(FileBasedFileSystem.java:306)
        at org.openide.loaders.DataNode.getIcon(DataNode.java:251)
        at org.openide.text.DataEditorSupport.initializeCloneableEditor(DataEditorSupport.java:288)
        at org.openide.text.CloneableEditorSupport.createPane(CloneableEditorSupport.java:1216)
        at org.openide.text.CloneableEditorSupport.createCloneableTopComponent(CloneableEditorSupport.java:1208)
        at org.openide.windows.CloneableOpenSupport.openCloneableTopComponent(CloneableOpenSupport.java:197)
        at org.openide.windows.CloneableOpenSupport$1.run(CloneableOpenSupport.java:98)
        at org.openide.util.Mutex.doEvent(Mutex.java:1335)
        at org.openide.util.Mutex.writeAccess(Mutex.java:452)
        at org.openide.windows.CloneableOpenSupport.open(CloneableOpenSupport.java:95)
        at org.openide.text.CloneableEditorSupport.open(CloneableEditorSupport.java:436)
        at org.openide.actions.OpenAction.performAction(OpenAction.java:81)
        at org.openide.util.actions.NodeAction$DelegateAction$1.run(NodeAction.java:589)
        at org.netbeans.modules.openide.util.ActionsBridge.doPerformAction(ActionsBridge.java:77)
        at org.openide.util.actions.NodeAction$DelegateAction.actionPerformed(NodeAction.java:585)
        at org.netbeans.modules.openfile.DefaultOpenFileImpl.open(DefaultOpenFileImpl.java:572)
        at org.netbeans.modules.openfile.OpenFile.open(OpenFile.java:72)
        at org.netbeans.modules.openfile.DefaultExternalDropHandler.openFile(DefaultExternalDropHandler.java:199)
        at org.netbeans.modules.openfile.DefaultExternalDropHandler.handleDrop(DefaultExternalDropHandler.java:122)
        at org.netbeans.core.windows.view.EditorView$EditorAreaComponent$1.drop(EditorView.java:253)
        at java.awt.dnd.DropTarget.drop(DropTarget.java:434)
        at sun.awt.dnd.SunDropTargetContextPeer.processDropMessage(SunDropTargetContextPeer.java:500)
        at sun.awt.dnd.SunDropTargetContextPeer$EventDispatcher.dispatchDropEvent(SunDropTargetContextPeer.java:812)
        at sun.awt.dnd.SunDropTargetContextPeer$EventDispatcher.dispatchEvent(SunDropTargetContextPeer.java:736)
        at sun.awt.dnd.SunDropTargetEvent.dispatch(SunDropTargetEvent.java:30)
        at java.awt.Component.dispatchEventImpl(Component.java:4440)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4413)
        at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4556)
        at java.awt.LightweightDispatcher.processDropTargetEvent(LightweightDispatcher.java:4291)
        at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:4145)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2475)
        at java.awt.Component.dispatchEvent(Component.java:4413)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)