java.util.ConcurrentModificationException
        at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449)
        at java.util.AbstractList$Itr.next(AbstractList.java:420)
        at org.netbeans.modules.ruby.platform.gems.GemPanel.notifyGemsUpdated(GemPanel.java:353)
        at org.netbeans.modules.ruby.platform.gems.GemPanel.access$1200(GemPanel.java:96)
        at org.netbeans.modules.ruby.platform.gems.GemPanel$4$1.run(GemPanel.java:1209)
        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.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:835)
        at org.netbeans.core.windows.services.NbPresenter.doShow(NbPresenter.java:869)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:857)
        at org.netbeans.core.windows.services.NbPresenter.run(NbPresenter.java:108)
        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:842)
        at java.awt.Component.show(Component.java:1302)
        at java.awt.Component.setVisible(Component.java:1255)
        at org.netbeans.modules.ruby.platform.gems.GemAction.showGemManager(GemAction.java:98)
        at org.netbeans.modules.ruby.platform.gems.GemAction.showGemManager(GemAction.java:60)
        at org.netbeans.modules.ruby.platform.gems.GemAction.performAction(GemAction.java:56)
        at org.openide.util.actions.CallableSystemAction$1.run(CallableSystemAction.java:118)
        at org.netbeans.modules.openide.util.ActionsBridge.doPerformAction(ActionsBridge.java:77)
        at org.openide.util.actions.CallableSystemAction.actionPerformed(CallableSystemAction.java:114)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1849)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2169)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
        at javax.swing.AbstractButton.doClick(AbstractButton.java:302)
        at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:1051)
        at javax.swing.plaf.basic.BasicPopupMenuUI$Actions.doReturn(BasicPopupMenuUI.java:441)
        at javax.swing.plaf.basic.BasicPopupMenuUI$Actions.actionPerformed(BasicPopupMenuUI.java:415)
        at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1571)
        at javax.swing.JComponent.processKeyBinding(JComponent.java:2772)
        at javax.swing.KeyboardManager.fireBinding(KeyboardManager.java:255)
        at javax.swing.KeyboardManager.fireKeyboardAction(KeyboardManager.java:204)
        at javax.swing.JComponent.processKeyBindingsForAllComponents(JComponent.java:2849)
        at javax.swing.JComponent.processKeyBindings(JComponent.java:2841)
        at javax.swing.JComponent.processKeyEvent(JComponent.java:2735)
        at java.awt.Component.processEvent(Component.java:5294)
        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.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1826)
        at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:681)
        at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:938)
        at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:810)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:645)
        at java.awt.Component.dispatchEventImpl(Component.java:3857)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        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.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)