From a new document, Properties section expanded by default.
Drop a Button.
Click in the fx:id ComboBox, type "tree", than the "End" key.
Resize the Button from the Content view.
You will get the following NPE.

[java] Glass detected outstanding Java exception at -[GlassViewDelegate sendJavaMouseEvent:]:src/com/sun/mat/ui/GlassViewDelegate.m:560
     [java] Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
     [java] at com.oracle.javafx.authoring.stage.v2.gesture.ResizeGesture.update(ResizeGesture.java:314)
     [java] at com.oracle.javafx.authoring.stage.v2.gesture.ResizeGesture.handleMouseDragged(ResizeGesture.java:235)
     [java] at com.oracle.javafx.authoring.stage.v2.gesture.ResizeGesture.handleMouseEvent(ResizeGesture.java:96)
     [java] at com.oracle.javafx.authoring.stage.v2.EditModeController.handleMouseEvent(EditModeController.java:212)
     [java] at com.oracle.javafx.authoring.stage.v2.EditModeController$1.handle(EditModeController.java:103)
     [java] at com.oracle.javafx.authoring.stage.v2.EditModeController$1.handle(EditModeController.java:100)
     [java] at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:69)
     [java] at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
     [java] at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
     [java] at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
     [java] at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
     [java] at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
     [java] at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
     [java] at javafx.event.Event.fireEvent(Event.java:171)
     [java] at javafx.scene.Scene$MouseHandler.process(Scene.java:3303)
     [java] at javafx.scene.Scene$MouseHandler.process(Scene.java:3143)
     [java] at javafx.scene.Scene$MouseHandler.access$1900(Scene.java:3098)
     [java] at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1525)
     [java] at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2241)
     [java] at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:227)
     [java] at com.sun.glass.ui.View.handleMouseEvent(View.java:528)
     [java] at com.sun.glass.ui.View.notifyMouse(View.java:921)