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:346)
        at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:643)
        at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:632)
        at org.openide.util.Mutex.writeAccess(Mutex.java:433)
        at org.netbeans.api.project.ProjectManager.saveProject(ProjectManager.java:632)
        at org.netbeans.modules.java.j2seproject.ui.customizer.J2SEProjectProperties.save(J2SEProjectProperties.java:443)
        at org.netbeans.modules.java.j2seproject.ui.customizer.CustomizerProviderImpl$StoreListener.actionPerformed(CustomizerProviderImpl.java:160)
        at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2$1.run(CustomizerDialog.java:277)
        at org.openide.util.Mutex.writeAccess(Mutex.java:394)
        at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2.run(CustomizerDialog.java:273)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:577)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1030)
Caused: org.openide.util.RequestProcessor$Item: task failed due to: java.lang.AssertionError
        at org.openide.util.RequestProcessor.post(RequestProcessor.java:267)
        at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener.actionPerformed(CustomizerDialog.java:270)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6216)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
        at java.awt.Component.processEvent(Component.java:5981)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4583)
        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.processMouseEvent(LightweightDispatcher.java:4220)
        at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:4150)
        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)