CheckComboBoxTableCell Exception

gistfile1.txt

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
	at com.sun.javafx.scene.control.skin.ComboBoxPopupControl.positionAndShowPopup(ComboBoxPopupControl.java:197)
	at com.sun.javafx.scene.control.skin.ComboBoxPopupControl.show(ComboBoxPopupControl.java:170)
	at com.sun.javafx.scene.control.skin.ComboBoxBaseSkin.handleControlPropertyChanged(ComboBoxBaseSkin.java:127)
	at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.handleControlPropertyChanged(ComboBoxListViewSkin.java:159)
	at com.sun.javafx.scene.control.skin.BehaviorSkinBase.lambda$registerChangeListener$61(BehaviorSkinBase.java:197)
	at com.sun.javafx.scene.control.MultiplePropertyChangeListenerHandler$1.changed(MultiplePropertyChangeListenerHandler.java:55)
	at javafx.beans.value.WeakChangeListener.changed(WeakChangeListener.java:89)
	at com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(ExpressionHelper.java:182)
	at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:81)
	at javafx.beans.property.ReadOnlyBooleanPropertyBase.fireValueChangedEvent(ReadOnlyBooleanPropertyBase.java:72)
	at javafx.beans.property.ReadOnlyBooleanWrapper.fireValueChangedEvent(ReadOnlyBooleanWrapper.java:103)
	at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:110)
	at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:144)
	at javafx.scene.control.ComboBoxBase.setShowing(ComboBoxBase.java:185)
	at javafx.scene.control.ComboBoxBase.show(ComboBoxBase.java:391)
	at com.sun.javafx.scene.control.behavior.ComboBoxBaseBehavior.show(ComboBoxBaseBehavior.java:286)
	at com.sun.javafx.scene.control.behavior.ComboBoxBaseBehavior.mouseReleased(ComboBoxBaseBehavior.java:241)
	at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
	at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
	at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
	at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
	at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
	at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
	at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
	at javafx.event.Event.fireEvent(Event.java:198)
	at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
	at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
	at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
	at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:381)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:417)
	at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
	at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
	at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
	at com.sun.glass.ui.View.notifyMouse(View.java:937)
	at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
	at java.lang.Thread.run(Thread.java:748)

Here's the MCVE to play around with.

Here's an animation of how to replicate it: