Start Ensemble8, scroll down to Advanced Stage sample, run it.
Click Create a Stage button, click close in the appeared stage, observe an NPE:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.glass.ui.TouchInputSupport.notifyBeginTouchEvent(TouchInputSupport.java:82)
at com.sun.glass.ui.mac.MacTouchInputSupport.notifyNextTouchEvent(MacTouchInputSupport.java:128)
at com.sun.glass.ui.mac.MacGestureSupport.notifyNextTouchEvent(MacGestureSupport.java:77)
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.glass.ui.TouchInputSupport.notifyBeginTouchEvent(TouchInputSupport.java:82)
at com.sun.glass.ui.mac.MacTouchInputSupport.notifyEndTouchEvent(MacTouchInputSupport.java:85)
at com.sun.glass.ui.mac.MacGestureSupport.notifyEndTouchEvent(MacGestureSupport.java:81)
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.glass.ui.TouchInputSupport.notifyBeginTouchEvent(TouchInputSupport.java:82)
at com.sun.glass.ui.mac.MacTouchInputSupport.notifyEndTouchEvent(MacTouchInputSupport.java:85)
at com.sun.glass.ui.mac.MacGestureSupport.notifyEndTouchEvent(MacGestureSupport.java:81)
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.glass.ui.TouchInputSupport.notifyBeginTouchEvent(TouchInputSupport.java:82)
at com.sun.glass.ui.mac.MacTouchInputSupport.notifyEndTouchEvent(MacTouchInputSupport.java:85)
at com.sun.glass.ui.mac.MacGestureSupport.notifyEndTouchEvent(MacGestureSupport.java:81)
.....

Sometimes after that I also get this, but it's quite rare, I'm not sure how to reliably reproduce it:

Exception in thread "JavaFX Application Thread" java.lang.NegativeArraySizeException
        at javafx.scene.Scene$ScenePeerListener.touchEventBegin(Scene.java:2631)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$9.run(GlassViewEventHandler.java:916)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$9.run(GlassViewEventHandler.java:912)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleBeginTouchEvent(GlassViewEventHandler.java:912) at com.sun.glass.ui.View.handleBeginTouchEvent(View.java:541)
        at com.sun.glass.ui.View.notifyBeginTouchEvent(View.java:1005)
        at com.sun.glass.ui.TouchInputSupport.notifyBeginTouchEvent(TouchInputSupport.java:81)
        at com.sun.glass.ui.mac.MacTouchInputSupport.notifyEndTouchEvent(MacTouchInputSupport.java:85)
        at com.sun.glass.ui.mac.MacGestureSupport.notifyEndTouchEvent(MacGestureSupport.java:81)