[Accessibility] HelloSpinner throws NPE when using primary action on the ComboBox

JFX build: 8u40 b09

Steps to reproduce:
1. Start Narrator on Windows 8.1.
2. Run HelloSpinner
3. Focus on "Value Factory:" ComboBox
4. Press "Caps Lock + SpaceBar", the primary action to open the menu. The menu is opened.
5. Press "Caps Lock + SpaceBar" again. NPE is thrown.

It seems to be a problem with ComboBox, but other ComboBox samples work fine. And HelloSpinner works fine without Narrator. I have not tried with VoiceOver yet.

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
        at HelloSpinner.lambda$start$2(HelloSpinner.java:62)
        at HelloSpinner$$Lambda$79/29392965.changed(Unknown Source)
        at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:361)
        at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:81)
        at javafx.beans.property.ReadOnlyObjectWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyObjectWrapper.java:176)
        at javafx.beans.property.ReadOnlyObjectWrapper.fireValueChangedEvent(ReadOnlyObjectWrapper.java:142)
        at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
        at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:146)
        at javafx.scene.control.SelectionModel.setSelectedItem(SelectionModel.java:102)
        at javafx.scene.control.ComboBox$ComboBoxSelectionModel.lambda$new$156(ComboBox.java:500)
        at javafx.scene.control.ComboBox$ComboBoxSelectionModel$$Lambda$76/29441439.invalidated(Unknown Source)
        at com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(ExpressionHelper.java:137)
        at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:81)
        at javafx.beans.property.ReadOnlyIntegerWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyIntegerWrapper.java:176)
        at javafx.beans.property.ReadOnlyIntegerWrapper.fireValueChangedEvent(ReadOnlyIntegerWrapper.java:142)
        at javafx.beans.property.IntegerPropertyBase.markInvalid(IntegerPropertyBase.java:113)
        at javafx.beans.property.IntegerPropertyBase.set(IntegerPropertyBase.java:147)
        at javafx.scene.control.SelectionModel.setSelectedIndex(SelectionModel.java:68)
        at javafx.scene.control.SingleSelectionModel.updateSelectedIndex(SingleSelectionModel.java:215)
        at javafx.scene.control.SingleSelectionModel.clearSelection(SingleSelectionModel.java:68)
        at javafx.scene.control.SingleSelectionModel.select(SingleSelectionModel.java:144)
        at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.lambda$createListView$322(ComboBoxListViewSkin.java:663)
        at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin$$Lambda$128/20633701.invalidated(Unknown Source)
        at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:349)
        at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:81)
        at javafx.beans.property.ReadOnlyIntegerWrapper$ReadOnlyPropertyImpl.fireValueChangedEvent(ReadOnlyIntegerWrapper.java:176)
        at javafx.beans.property.ReadOnlyIntegerWrapper.fireValueChangedEvent(ReadOnlyIntegerWrapper.java:142)
        at javafx.beans.property.IntegerPropertyBase.markInvalid(IntegerPropertyBase.java:113)
        at javafx.beans.property.IntegerPropertyBase.set(IntegerPropertyBase.java:147)
        at javafx.scene.control.SelectionModel.setSelectedIndex(SelectionModel.java:68)
        at javafx.scene.control.MultipleSelectionModelBase.clearSelection(MultipleSelectionModelBase.java:626)
        at com.sun.javafx.scene.control.skin.ListViewSkin.executeAccessibleAction(ListViewSkin.java:548)
        at javafx.scene.control.Control.executeAccessibleAction(Control.java:913)
        at javafx.scene.Node$19.executeAction(Node.java:9628)
        at com.sun.glass.ui.Accessible$ExecuteAction.run(Accessible.java:177)
        at com.sun.glass.ui.Accessible$ExecuteAction.run(Accessible.java:173)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.glass.ui.Accessible.lambda$executeAction$5(Accessible.java:190)
        at com.sun.glass.ui.Accessible$$Lambda$225/4743536.get(Unknown Source)
        at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:387)
        at com.sun.glass.ui.Accessible.executeAction(Accessible.java:187)
        at com.sun.glass.ui.win.WinAccessible.changeSelection(WinAccessible.java:543)
        at com.sun.glass.ui.win.WinAccessible.Select(WinAccessible.java:1296)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.lambda$null$143(WinApplication.java:101)
        at com.sun.glass.ui.win.WinApplication$$Lambda$36/24025819.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:745)