java.lang.NullPointerException
        at org.netbeans.modules.gsfret.source.CacheClassPath.<init>(CacheClassPath.java:90)
        at org.netbeans.modules.gsfret.source.CacheClassPath.forBootPath(CacheClassPath.java:194)
        at org.netbeans.napi.gsfret.source.ClasspathInfo.<init>(ClasspathInfo.java:109)
        at org.netbeans.napi.gsfret.source.ClasspathInfo.create(ClasspathInfo.java:183)
        at org.netbeans.modules.refactoring.ruby.RetoucheUtils.getClasspathInfoFor(RetoucheUtils.java:446)
        at org.netbeans.modules.refactoring.ruby.RetoucheUtils.getClasspathInfoFor(RetoucheUtils.java:451)
        at org.netbeans.modules.refactoring.ruby.ui.WhereUsedQueryUI.<init>(WhereUsedQueryUI.java:74)
        at org.netbeans.modules.refactoring.ruby.ui.RefactoringActionsProvider$3.createRefactoringUI(RefactoringActionsProvider.java:245)
        at org.netbeans.modules.refactoring.ruby.ui.RefactoringActionsProvider$TextComponentTask.run(RefactoringActionsProvider.java:505)
        at org.netbeans.modules.refactoring.ruby.ui.RefactoringActionsProvider$TextComponentTask.run(RefactoringActionsProvider.java:472)
        at org.netbeans.napi.gsfret.source.Source.runUserActionTask(Source.java:470)
        at org.netbeans.modules.refactoring.ruby.ui.RefactoringActionsProvider$TextComponentTask.run(RefactoringActionsProvider.java:511)
        at org.netbeans.modules.refactoring.ruby.ui.RefactoringActionsProvider.doFindUsages(RefactoringActionsProvider.java:257)
        at org.netbeans.modules.refactoring.api.impl.ActionsImplementationFactory.doFindUsages(ActionsImplementationFactory.java:87)
        at org.netbeans.modules.refactoring.spi.impl.WhereUsedAction.performAction(WhereUsedAction.java:62)
        at org.netbeans.modules.refactoring.spi.impl.RefactoringGlobalAction$ContextAction.actionPerformed(RefactoringGlobalAction.java:177)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1882)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2202)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
        at javax.swing.AbstractButton.doClick(AbstractButton.java:334)
        at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1051)
        at apple.laf.CUIAquaMenuItem.doClick(CUIAquaMenuItem.java:119)
        at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:1092)
        at java.awt.Component.processMouseEvent(Component.java:5602)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3135)
        at java.awt.Component.processEvent(Component.java:5367)
        at java.awt.Container.processEvent(Container.java:2010)
        at java.awt.Component.dispatchEventImpl(Component.java:4068)
        at java.awt.Container.dispatchEventImpl(Container.java:2068)
        at java.awt.Component.dispatchEvent(Component.java:3903)
        at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4256)
        at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:3936)
        at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:3866)
        at java.awt.Container.dispatchEventImpl(Container.java:2054)
        at java.awt.Window.dispatchEventImpl(Window.java:1791)
        at java.awt.Component.dispatchEvent(Component.java:3903)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:176)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)