ADDITIONAL SYSTEM INFORMATION :
macOS 10.15.4, JDK 15 EAB 21

A DESCRIPTION OF THE PROBLEM :
When I use the cross-platform LAF (Look and Feel) and select a JComboBox displayed using a Frame, a NullPointerException is thrown. This does not occur when I do not set the LAF. Here is the stack trace:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.desktop/com.apple.laf.AquaMenuPainter.paintSelectedMenuItemBackground(AquaMenuPainter.java:157)
at java.desktop/com.apple.laf.AquaComboBoxRendererInternal.paintComponent(AquaComboBoxRendererInternal.java:147)
at java.desktop/javax.swing.JComponent.paint(JComponent.java:1074)
at java.desktop/javax.swing.CellRendererPane.paintComponent(CellRendererPane.java:165)
at java.desktop/javax.swing.plaf.basic.BasicListUI.paintCell(BasicListUI.java:288)
at java.desktop/javax.swing.plaf.basic.BasicListUI.paintImpl(BasicListUI.java:378)
at java.desktop/javax.swing.plaf.basic.BasicListUI.paint(BasicListUI.java:301)
at java.desktop/javax.swing.plaf.ComponentUI.update(ComponentUI.java:161)
at java.desktop/javax.swing.JComponent.paintComponent(JComponent.java:797)
at java.desktop/javax.swing.JComponent.paint(JComponent.java:1074)
at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
at java.desktop/javax.swing.JComponent.paint(JComponent.java:1083)
at java.desktop/javax.swing.JViewport.paint(JViewport.java:737)
at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
at java.desktop/javax.swing.JComponent.paint(JComponent.java:1083)
at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
at java.desktop/javax.swing.JComponent.paint(JComponent.java:1083)
at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
at java.desktop/javax.swing.JComponent.paint(JComponent.java:1083)
at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
at java.desktop/javax.swing.JComponent.paint(JComponent.java:1083)
at java.desktop/javax.swing.JLayeredPane.paint(JLayeredPane.java:586)
at java.desktop/javax.swing.JComponent.paintChildren(JComponent.java:907)
at java.desktop/javax.swing.JComponent.paintToOffscreen(JComponent.java:5262)
at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBufferedImpl(RepaintManager.java:1643)
at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1618)
at java.desktop/javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1556)
at java.desktop/javax.swing.RepaintManager.paint(RepaintManager.java:1323)
at java.desktop/javax.swing.JComponent.paint(JComponent.java:1060)
at java.desktop/java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
at java.desktop/sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:75)
at java.desktop/sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:112)
at java.desktop/java.awt.Container.paint(Container.java:2002)
at java.desktop/java.awt.Window.paint(Window.java:3928)
at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:876)
at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:848)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:848)
at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:823)
at java.desktop/javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:772)
at java.desktop/javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1884)
at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:316)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Compile and run the source code given
2. Click on the JComboBox on the form
3. A NullPointerException is thrown and the list of items of the combo box are blank (like a gray rectangle)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expect the cross-platform LAF to behave like the default, and display the items of the combo box when I click on it.
ACTUAL -
A NullPointerException is thrown and the list of items of the combo box are blank. When I attempt to click on the combo box again, the items do appear, but additional NullPointerExceptions are thrown.

---------- BEGIN SOURCE ----------
import javax.swing.*;

public class Bar {
    public static void main(String[] args) {
        JComboBox<String> comboBox = new JComboBox<>();
        JPanel panel = new JPanel();
        JFrame frame = new JFrame();

        try {
            UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
        } catch (Exception e) {
            e.printStackTrace();

            return;
        } //end try catch

        comboBox.addItem("Foo");

        comboBox.addItem("Bar");

        comboBox.addItem("Baz");

        panel.add(comboBox);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.setLocationRelativeTo(null);

        frame.setContentPane(panel);

        frame.pack();

        frame.setVisible(true);
    } //main
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
If I do not set the LAF of the form, the error does not occur.

FREQUENCY : always