presidio-graphics-scrum build #2476

Saw this while doing integration testing. This is a regression.

To reproduce:
Create 2 more popup windows, then close the main window.

bash-4.1$ java -cp "../../../artifacts/sdk/rt/lib/jfxrt.jar;dist/HelloWorld.jar
" helloworld.HelloPopup
W: javafx.stage.Popup
W: javafx.stage.Stage
W: javafx.stage.Popup
W: javafx.stage.Popup
W: javafx.stage.Stage
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
        at com.sun.javafx.binding.ExpressionHelper$MultipleInvalidationMultipleC
hange.fireValueChangedEvent(ExpressionHelper.java:512)
        at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Express
ionHelper.java:61)
        at javafx.beans.property.BooleanPropertyBase.fireValueChangedEvent(Boole
anPropertyBase.java:70)
        at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanProperty
Base.java:77)
        at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.jav
a:110)
        at javafx.stage.Window.setFocused(Window.java:247)
        at javafx.stage.PopupWindow.impl_visibleChanged(PopupWindow.java:318)
        at javafx.stage.Window$13.invalidated(Window.java:558)
        at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanProperty
Base.java:76)
        at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.jav
a:110)
        at javafx.stage.Window.setVisible(Window.java:561)
        at javafx.stage.PopupWindow.doAutoHide(PopupWindow.java:352)
        at com.sun.javafx.stage.PopupEventRedirector.handleFocusUngrabEvent(Popu
pEventRedirector.java:112)
        at com.sun.javafx.stage.PopupEventRedirector.handleRedirectedEvent(Popup
EventRedirector.java:52)
        at com.sun.javafx.event.EventRedirector.dispatchCapturingEvent(EventRedi
rector.java:85)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchCapturingEvent(
CompositeEventDispatcher.java:22)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDis
patcher.java:31)
        at com.sun.javafx.event.EventRedirector.redirectEvent(EventRedirector.ja
va:103)
        at com.sun.javafx.event.EventRedirector.dispatchCapturingEvent(EventRedi
rector.java:82)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchCapturingEvent(
CompositeEventDispatcher.java:22)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDis
patcher.java:31)