I am using JavaFX 8u20-ea-b16 with a JavaFX+Swing application on Ubuntu 14.04. I saw these exceptions occasionally on shutdown in 8u5, and I saw it again in in 8u20-ea-b16 so thought I'd report it. It is mentioned as a sidenote in RT-37075, but I gather that ticket was already fixed in -ea-b16 (see comments on RT-32050). It's fairly benign as it only shows up on shutdown and doesn't seem to cause any problems:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.javafx.tk.quantum.QuantumToolkit.isSupported(QuantumToolkit.java:1073)
at com.sun.javafx.application.PlatformImpl.isSupportedImpl(PlatformImpl.java:759)
at com.sun.javafx.application.PlatformImpl.isSupported(PlatformImpl.java:472)
at javafx.application.Platform.isSupported(Platform.java:166)
at com.sun.javafx.scene.input.PickResultChooser.processOffer(PickResultChooser.java:180)
at com.sun.javafx.scene.input.PickResultChooser.offer(PickResultChooser.java:142)
at javafx.scene.Node.impl_intersects(Node.java:4753)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2939)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2933)
at javafx.scene.Node.impl_pickNode(Node.java:4722)
at javafx.scene.Scene$MouseHandler.pickNode(Scene.java:3866)
at javafx.scene.Scene$MouseHandler.access$1600(Scene.java:3452)
at javafx.scene.Scene.pick(Scene.java:1908)
at javafx.scene.Scene.access$6700(Scene.java:144)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3678)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3452)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1728)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2461)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:348)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:273)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:382)
at com.sun.glass.ui.View.handleMouseEvent(View.java:553)
at com.sun.glass.ui.View.notifyMouse(View.java:925)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
at com.sun.glass.ui.gtk.GtkApplication.lambda$null$45(GtkApplication.java:126)
at com.sun.glass.ui.gtk.GtkApplication$$Lambda$43/32872801.run(Unknown Source)
at java.lang.Thread.run(Thread.java:745)