java.lang.NullPointerException: This exception has no message.

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java.lang.NullPointerException:
at net.sf.robocode.repository.root.ClassPathRoot.visitDirectory(ClassPathRoot.java:82)
at net.sf.robocode.repository.root.ClassPathRoot.update(ClassPathRoot.java:51)
at net.sf.robocode.repository.root.handlers.ClassPathHandler.visitDirectory(ClassPathHandler.java:36)
at net.sf.robocode.repository.root.handlers.RootHandler.visitDirectories(RootHandler.java:35)
at net.sf.robocode.repository.Database.update(Database.java:48)
at net.sf.robocode.repository.RepositoryManager.refresh(RepositoryManager.java:97)
at net.sf.robocode.repository.RepositoryManager.reload(RepositoryManager.java:121)
at net.sf.robocode.repository.RepositoryManager$1.settingChanged(RepositoryManager.java:52)
at net.sf.robocode.settings.SettingsManager.notifyPropertyChanged(SettingsManager.java:1044)
at net.sf.robocode.settings.SettingsManager.access$100(SettingsManager.java:58)
at net.sf.robocode.settings.SettingsManager$SortedProperties.setProperty(SettingsManager.java:1083)
at net.sf.robocode.settings.SettingsManager.setOptionsDevelopmentPath(SettingsManager.java:852)
at net.sf.robocode.ui.dialog.PreferencesDevelopmentOptionsTab.storePreferences(PreferencesDevelopmentOptionsTab.java:179)
at net.sf.robocode.ui.dialog.PreferencesDialog.finishButtonActionPerformed(PreferencesDialog.java:153)
at net.sf.robocode.ui.dialog.WizardController.finishButtonActionPerformed(WizardController.java:68)
at net.sf.robocode.ui.dialog.WizardController.access$1(WizardController.java:67)
at net.sf.robocode.ui.dialog.WizardController$EventHandler.actionPerformed(WizardController.java:45)
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:6263)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6028)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4630)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2475)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:178)
at java.awt.Dialog$1.run(Dialog.java:1045)
at java.awt.Dialog$3.run(Dialog.java:1097)
at java.security.AccessController.doPrivileged(Native Method)
at java.awt.Dialog.show(Dialog.java:1095)
at java.awt.Component.show(Component.java:1563)
at java.awt.Component.setVisible(Component.java:1515)
at java.awt.Window.setVisible(Window.java:841)
at java.awt.Dialog.setVisible(Dialog.java:985)
at net.sf.robocode.ui.dialog.WindowUtil.packCenterShow(WindowUtil.java:143)
at net.sf.robocode.ui.WindowManager.showOptionsPreferences(WindowManager.java:274)
at net.sf.robocode.ui.dialog.MenuBar.optionsPreferencesActionPerformed(MenuBar.java:904)
at net.sf.robocode.ui.dialog.MenuBar.access$23(MenuBar.java:903)
at net.sf.robocode.ui.dialog.MenuBar$EventHandler.actionPerformed(MenuBar.java:140)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.AbstractButton.doClick(AbstractButton.java:357)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1225)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1266)
at java.awt.Component.processMouseEvent(Component.java:6263)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6028)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4630)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
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)

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