FULL PRODUCT VERSION :
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) Client VM (build 25.45-b02, mixed mode)

java 8u20, 8u31, 8u40

ADDITIONAL OS VERSION INFORMATION :
windows 7 6.1.7601
windows 8 6.3.9600

A DESCRIPTION OF THE PROBLEM :
There are various nullpointerexception when using jfxpanel. Exceptions occur when setting up jfxpanel with fx components or when closing parent frame.

 Might be threading/synchronization issue since jfxpanel has to handle swing and fx.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and run code sample.
Click the FX button.
New internal frame opens.
Console prints exception.
Close internal frame.
Console prints exception.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No exception
ACTUAL -
exception when adding jfxpanel and closing jfxpanel depending on java version and os

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Occurs when click button to launch internal frame

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javafx.embed.swing.JFXPanel$HostContainer.lambda$setEmbeddedStage$52(JFXPanel.java:915)
        at javafx.embed.swing.JFXPanel$HostContainer$$Lambda$93/32395568.run(Unknown Source)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
        at java.awt.EventQueue.access$500(EventQueue.java:97)
        at java.awt.EventQueue$3.run(EventQueue.java:709)
        at java.awt.EventQueue$3.run(EventQueue.java:703)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
        at java.awt.EventQueue$4.run(EventQueue.java:731)
        at java.awt.EventQueue$4.run(EventQueue.java:729)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)



Occurs when closing internal frame

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javafx.embed.swing.JFXPanel.getInputMethodRequests(JFXPanel.java:858)
        at sun.awt.im.InputMethodAdapter.haveActiveClient(InputMethodAdapter.java:61)
        at sun.awt.windows.WInputMethod.deactivate(WInputMethod.java:340)
        at sun.awt.im.InputContext.deactivateInputMethod(InputContext.java:492)
        at sun.awt.im.InputContext.focusLost(InputContext.java:458)
        at sun.awt.im.InputContext.removeNotify(InputContext.java:627)
        at java.awt.Component.removeNotify(Component.java:7010)
        at java.awt.Container.removeNotify(Container.java:2820)
        at javax.swing.JComponent.removeNotify(JComponent.java:4767)
        at javafx.embed.swing.JFXPanel.removeNotify(JFXPanel.java:880)
        at java.awt.Container.removeNotify(Container.java:2804)
        at javax.swing.JComponent.removeNotify(JComponent.java:4767)
        at java.awt.Container.removeNotify(Container.java:2804)
        at javax.swing.JComponent.removeNotify(JComponent.java:4767)
        at java.awt.Container.removeNotify(Container.java:2804)
        at javax.swing.JComponent.removeNotify(JComponent.java:4767)
        at javax.swing.JRootPane.removeNotify(JRootPane.java:765)
        at java.awt.Container.removeNotify(Container.java:2804)
        at javax.swing.JComponent.removeNotify(JComponent.java:4767)
        at java.awt.Container.remove(Container.java:1204)
        at javax.swing.JLayeredPane.remove(JLayeredPane.java:246)
        at javax.swing.JDesktopPane.remove(JDesktopPane.java:505)
        at java.awt.Container.remove(Container.java:1262)
        at javax.swing.JDesktopPane.remove(JDesktopPane.java:436)
        at javax.swing.DefaultDesktopManager.closeFrame(DefaultDesktopManager.java:100)
        at javax.swing.plaf.basic.BasicInternalFrameUI.closeFrame(BasicInternalFrameUI.java:547)
        at javax.swing.plaf.basic.BasicInternalFrameUI$Handler.propertyChange(BasicInternalFrameUI.java:1410)
        at java.beans.PropertyChangeSupport.fire(PropertyChangeSupport.java:335)
        at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:327)
        at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:263)
        at java.awt.Component.firePropertyChange(Component.java:8422)
        at javax.swing.JInternalFrame.doDefaultCloseAction(JInternalFrame.java:1634)
        at javax.swing.plaf.basic.BasicInternalFrameTitlePane$CloseAction.actionPerformed(BasicInternalFrameTitlePane.java:619)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
        at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289)
        at java.awt.Component.processMouseEvent(Component.java:6525)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
        at java.awt.Component.processEvent(Component.java:6290)
        at java.awt.Container.processEvent(Container.java:2234)
        at java.awt.Component.dispatchEventImpl(Component.java:4881)
        at java.awt.Container.dispatchEventImpl(Container.java:2292)
        at java.awt.Component.dispatchEvent(Component.java:4703)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
        at java.awt.Container.dispatchEventImpl(Container.java:2278)
        at java.awt.Window.dispatchEventImpl(Window.java:2750)
        at java.awt.Component.dispatchEvent(Component.java:4703)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
        at java.awt.EventQueue.access$500(EventQueue.java:97)
        at java.awt.EventQueue$3.run(EventQueue.java:709)
        at java.awt.EventQueue$3.run(EventQueue.java:703)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
        at java.awt.EventQueue$4.run(EventQueue.java:731)
        at java.awt.EventQueue$4.run(EventQueue.java:729)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.beans.PropertyVetoException;
import javax.swing.*;

import javafx.application.*;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.*;


public class SwingEmbedFX2 {
    protected static JFXPanel fxPanel;
    protected static JDesktopPane desktopPane;

    static void packInternalFrame(JInternalFrame iframe) {
        try {
            iframe.pack();
            iframe.setIcon(true);
            iframe.setMaximum(true);
            iframe.moveToFront();
            iframe.setVisible(true);

        // From setMaximum method call
        } catch (PropertyVetoException ex) {
            System.out.println(ex);
            ex.printStackTrace();
        }
   }

    static void launchFXFrame() {
        JInternalFrame iframe = new JInternalFrame(
            "FX Embedded", true, true, true);

        iframe.setLayout(new BorderLayout());
        desktopPane.add(iframe);

        try {
            iframe.setMaximum(true);
        // From setMaximum method call
        } catch (PropertyVetoException ex) {
            System.out.println(ex);
            ex.printStackTrace();
        }

        fxPanel = new JFXPanel();
        iframe.add(fxPanel, BorderLayout.CENTER);

        Platform.runLater(() -> createScene());
        packInternalFrame(iframe);
    }

    public static void runTest() {
        final JFrame f = new JFrame();

        f.setLayout(new BorderLayout());
        f.setSize(new Dimension(500, 500));
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        desktopPane = new JDesktopPane();
        f.getContentPane().add(BorderLayout.CENTER,
            new JScrollPane(desktopPane));

        JInternalFrame iframe = new JInternalFrame();
        iframe.setResizable(true);
        JButton btn = new JButton("FX");
        btn.addActionListener(a -> launchFXFrame());
        iframe.add(btn);
        desktopPane.add(iframe);
        iframe.pack();
        desktopPane.validate();
        iframe.setVisible(true);
        desktopPane.setVisible(true);
        f.setVisible(true);
    }

    public static void createScene() {
        StackPane fxRoot = new StackPane();
        fxPanel.setScene(new Scene(fxRoot));
        BorderPane bp = new BorderPane();
        fxRoot.getChildren().addAll(bp);
        bp.setCenter(new Label("FX Label"));
    }

    public static void main(String [] args) {
        try {
            SwingUtilities.invokeAndWait(() -> runTest());
        } catch (Exception ex) {
            System.out.println(ex);
            ex.printStackTrace();
        }

    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Moving packInternalFrame before creating scene helps depending on java version and possibly operating system.