java.lang.AssertionError
        at org.netbeans.spi.project.support.ant.ProjectProperties$PP.write(ProjectProperties.java:217)
        at org.netbeans.spi.project.support.ant.ProjectProperties.write(ProjectProperties.java:134)
        at org.netbeans.spi.project.support.ant.AntProjectHelper.save(AntProjectHelper.java:595)
        at org.netbeans.spi.project.support.ant.AntProjectHelper.access$100(AntProjectHelper.java:102)
        at org.netbeans.spi.project.support.ant.AntProjectHelper$1.save(AntProjectHelper.java:140)
        at org.netbeans.modules.project.ant.AntBasedProjectFactorySingleton.saveProject(AntBasedProjectFactorySingleton.java:337)
        at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:643)
        at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:632)
        at org.openide.util.Mutex.writeAccess(Mutex.java:433)
        at org.netbeans.api.project.ProjectManager.saveProject(ProjectManager.java:632)
        at org.netbeans.modules.projectapi.AuxiliaryConfigBasedPreferencesProvider.flushImpl(AuxiliaryConfigBasedPreferencesProvider.java:288)
        at org.netbeans.modules.projectapi.AuxiliaryConfigBasedPreferencesProvider.access$000(AuxiliaryConfigBasedPreferencesProvider.java:83)
        at org.netbeans.modules.projectapi.AuxiliaryConfigBasedPreferencesProvider$2.run(AuxiliaryConfigBasedPreferencesProvider.java:206)
        at org.netbeans.modules.projectapi.AuxiliaryConfigBasedPreferencesProvider$2.run(AuxiliaryConfigBasedPreferencesProvider.java:204)
        at org.openide.util.Mutex.writeAccess(Mutex.java:394)
        at org.netbeans.modules.projectapi.AuxiliaryConfigBasedPreferencesProvider.flush(AuxiliaryConfigBasedPreferencesProvider.java:204)
        at org.netbeans.modules.projectapi.AuxiliaryConfigBasedPreferencesProvider$AuxiliaryConfigBasedPreferences.flush(AuxiliaryConfigBasedPreferencesProvider.java:558)
        at org.netbeans.modules.web.client.tools.api.DebugProjectPanel$2.actionPerformed(DebugProjectPanel.java:158)
        at org.netbeans.core.windows.services.NbPresenter$ButtonListener.actionPerformed(NbPresenter.java:1266)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1849)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2169)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:5517)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3135)
        at java.awt.Component.processEvent(Component.java:5282)
        at java.awt.Container.processEvent(Container.java:1966)
        at java.awt.Component.dispatchEventImpl(Component.java:3984)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Component.dispatchEvent(Component.java:3819)
        at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4212)
        at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:3892)
        at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:3822)
        at java.awt.Container.dispatchEventImpl(Container.java:2010)
        at java.awt.Window.dispatchEventImpl(Window.java:1791)
        at java.awt.Component.dispatchEvent(Component.java:3819)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:153)
        at java.awt.Dialog$1.run(Dialog.java:535)
        at java.awt.Dialog$2.run(Dialog.java:565)
        at java.security.AccessController.doPrivileged(AccessController.java:0)
        at java.awt.Dialog.show(Dialog.java:563)
        at org.netbeans.core.windows.services.NbPresenter.superShow(NbPresenter.java:985)
        at org.netbeans.core.windows.services.NbPresenter.doShow(NbPresenter.java:1019)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:1007)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:115)
        at org.openide.util.Mutex.doEventAccess(Mutex.java:1355)
        at org.openide.util.Mutex.readAccess(Mutex.java:268)
        at org.netbeans.core.windows.services.NbPresenter.show(NbPresenter.java:992)
        at java.awt.Component.show(Component.java:1302)
        at java.awt.Component.setVisible(Component.java:1255)
        at org.netbeans.core.windows.services.DialogDisplayerImpl$1AWTQuery.showDialog(DialogDisplayerImpl.java:232)
        at org.netbeans.core.windows.services.DialogDisplayerImpl$1AWTQuery.run(DialogDisplayerImpl.java:165)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)