java.lang.AssertionError: Should be a folder: D:\projects\TutorialCalculator\build\web\WEB-INF\classes\calculator@c9e33b13:751176
   at org.netbeans.modules.masterfs.watcher.Watcher$Ext.unregister(Watcher.java:253)
   at org.netbeans.modules.masterfs.watcher.Watcher.unregister(Watcher.java:134)
   at org.netbeans.modules.masterfs.filebasedfs.fileobjects.BaseFileObj.removeFileChangeListener(BaseFileObj.java:508)
   at org.openide.filesystems.FileUtil$Holder.run(FileUtil.java:554)
   at org.openide.util.lookup.implspi.ActiveQueue$Impl.run(ActiveQueue.java:109)
   at java.lang.Thread.run(Thread.java:722)