Scenario:
(1) Creating a scene with a root.
(2) Setting another root for the scene.
(3) Resulting in NulpointerException

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at javafx.scene.Node.localToScreen(Node.java:4164)
at javafx.scene.Node.localToScreen(Node.java:4139)
at javafx.scene.web.WebView.processMouseEvent(WebView.java:987)
at javafx.scene.web.WebView.access$2500(WebView.java:76)
at javafx.scene.web.WebView$14.handle(WebView.java:1130)
at javafx.scene.web.WebView$14.handle(WebView.java:1128)
at com.sun.javafx.event.CompositeEventHandler$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.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:204)
at com.sun.javafx.event.EventQueue.fire(EventQueue.java:48)
at javafx.scene.Scene$MouseHandler.handleEnterExit(Scene.java:3662)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3787)
at javafx.scene.Scene$MouseHandler.access$1800(Scene.java:3471)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1695)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2486)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:314)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:243)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:345)
at com.sun.glass.ui.View.handleMouseEvent(View.java:526)
at com.sun.glass.ui.View.notifyMouse(View.java:898)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
at com.sun.glass.ui.win.WinApplication$4$1.run(WinApplication.java:112)
at java.lang.Thread.run(Thread.java:745)

In the class Node there is a check for "scene == null || window == null", but in the line above it states "window = scene.getWindow()". So if scene is null, it will cause a NullPointerException.