JFoenix NullPointerException in JFXDatePicker

问题

I use JFXDatePicker from JFoenix library for a Gluon project. I get an exception when trying to change month in JFXDatePicker get exception, which occurs the moment the month-change buttons are pressed. I can't take a screenshot because the pop-up of the open calendar disappears when I attempt it, so I've included inline below a pic from the Internet.

Code example of adding JFXDatePicker to VBox:

  @FXML
    private View primary;

    public void initialize() {
        VBox dateBox = new VBox();
        JFXDatePicker date = new JFXDatePicker();
        date.setValue(LocalDate.now());
        dateBox.getChildren().add(date);
        primary.getChildren().add(dateBox);
    }

Exception:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
    at com.jfoenix.skins.JFXButtonSkin$1.getMask(JFXButtonSkin.java:61)
    at com.jfoenix.controls.JFXRippler$RippleGenerator.createOverlay(JFXRippler.java:434)
    at com.jfoenix.controls.JFXRippler$RippleGenerator.createRipple(JFXRippler.java:388)
    at com.jfoenix.controls.JFXRippler.createRipple(JFXRippler.java:285)
    at com.jfoenix.controls.JFXRippler.lambda$initControlListeners$3(JFXRippler.java:273)
    at com.jfoenix.controls.JFXRippler$$Lambda$4.handle(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler$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.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    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:198)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
    at javafx.scene.Scene$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$345(GlassViewEventHandler.java:432)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication.lambda$null$203(GtkApplication.java:139)
    at java.lang.Thread.run(Thread.java:748)

来源：https://stackoverflow.com/questions/60160230/jfoenix-nullpointerexception-in-jfxdatepicker