同时关闭两个JavaFX应用程序

Question

我有两个不同的JavaFX程序正在运行。当一个关闭时，它也会向另一个应用程序发送一条消息以也关闭。如果我用Platform.exit()关闭了第一个应用程序，则当我用Platform.exit()关闭了第二个应用程序时，它关闭了，但是我得到了

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
    at com.sun.javafx.tk.quantum.QuantumToolkit.isSupported(QuantumToolkit.java:1153)
    at com.sun.javafx.application.PlatformImpl.isSupportedImpl(PlatformImpl.java:809)
    at com.sun.javafx.application.PlatformImpl.isSupported(PlatformImpl.java:482)
    at javafx.application.Platform.isSupported(Platform.java:168)
    at com.sun.javafx.scene.input.PickResultChooser.processOffer(PickResultChooser.java:182)
    at com.sun.javafx.scene.input.PickResultChooser.offer(PickResultChooser.java:143)
    at javafx.scene.Node.impl_intersects(Node.java:4945)
    at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2942)
    at javafx.scene.Node.impl_pickNode(Node.java:4914)
    at javafx.scene.layout.Region.impl_pickNodeLocal(Region.java:2936)
    at javafx.scene.Node.impl_pickNode(Node.java:4914)
    at javafx.scene.Scene$MouseHandler.pickNode(Scene.java:3899)
    at javafx.scene.Scene$MouseHandler.access$1600(Scene.java:3485)
    at javafx.scene.Scene.pick(Scene.java:1942)
    at javafx.scene.Scene.access$6700(Scene.java:159)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3711)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:394)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$353(GlassViewEventHandler.java:432)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$147(WinApplication.java:177)
    at java.lang.Thread.run(Unknown Source)

如果我使用System.exit(0)关闭第一个应用程序，则用Platform.exit()关闭第二个应用程序时不会出现此错误。

可能是什么问题？