java.lang.NullPointerException
        at javax.swing.plaf.basic.BasicComboBoxUI.isFocusTraversable(BasicComboBoxUI.java:834)
        at javax.swing.LayoutFocusTraversalPolicy.accept(LayoutFocusTraversalPolicy.java:218)
        at javax.swing.SortingFocusTraversalPolicy.getFirstComponent(SortingFocusTraversalPolicy.java:444)
        at javax.swing.LayoutFocusTraversalPolicy.getFirstComponent(LayoutFocusTraversalPolicy.java:148)
        at javax.swing.DefaultFocusManager.getFirstComponent(DefaultFocusManager.java:103)
        at javax.swing.LegacyGlueFocusTraversalPolicy.getFirstComponent(LegacyGlueFocusTraversalPolicy.java:115)
        at javax.swing.LegacyGlueFocusTraversalPolicy.getDefaultComponent(LegacyGlueFocusTraversalPolicy.java:133)
        at javax.swing.SortingFocusTraversalPolicy.enumerateAndSortCycle(SortingFocusTraversalPolicy.java:131)
        at javax.swing.SortingFocusTraversalPolicy.getComponentAfter(SortingFocusTraversalPolicy.java:244)
        at javax.swing.LayoutFocusTraversalPolicy.getComponentAfter(LayoutFocusTraversalPolicy.java:88)
        at javax.swing.DefaultFocusManager.getComponentAfter(DefaultFocusManager.java:61)
        at javax.swing.LegacyGlueFocusTraversalPolicy.getComponentAfter(LegacyGlueFocusTraversalPolicy.java:67)
        at java.awt.Component.nextFocusHelper(Component.java:6813)
        at java.awt.Container.nextFocusHelper(Container.java:3113)
        at java.awt.Component.removeNotify(Component.java:6062)
        at java.awt.Container.removeNotify(Container.java:2577)
        at javax.swing.JComponent.removeNotify(JComponent.java:4494)
        at java.awt.Container.removeNotify(Container.java:2571)
        at javax.swing.JComponent.removeNotify(JComponent.java:4494)
        at java.awt.Container.removeNotify(Container.java:2571)
        at javax.swing.JComponent.removeNotify(JComponent.java:4494)
        at java.awt.Container.removeNotify(Container.java:2571)
        at javax.swing.JComponent.removeNotify(JComponent.java:4494)
        at org.netbeans.core.windows.view.ui.toolbars.ToolbarContainer.removeNotify(ToolbarContainer.java:151)
        at java.awt.Container.remove(Container.java:1114)
        at java.awt.Container.remove(Container.java:1172)
        at java.awt.Container.addImpl(Container.java:1020)
        at java.awt.Container.add(Container.java:351)
        at org.netbeans.core.windows.view.ui.toolbars.ToolbarRow.drop(ToolbarRow.java:309)
        at org.netbeans.core.windows.view.ui.toolbars.DnDSupport.dragDropEnd(DnDSupport.java:192)
        at java.awt.dnd.DragSourceContext.dragDropEnd(DragSourceContext.java:399)
        at sun.awt.dnd.SunDragSourceContextPeer$EventDispatcher.run(SunDragSourceContextPeer.java:432)
        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: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)