Cannot find exception's cause

Question

I've tried to find some answered questions related to my problem, but i had not success.

In my application i get a strange java.lang.IllegalArgumentException, but i can't find the cause since in the stack trace there isn't any referrement to any code line. I also tried to catch the exception in every way i know, still nothing...

Here's my code :

import java.awt.*;
import java.awt.event.ActionEvent;
import java.util.*;
import javax.swing.*;
import javax.swing.border.LineBorder;
public class Test
{
    public static void main(String[] a){
        SwingUtilities.invokeLater(new Runnable(){
            public void run(){
                try{
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                    JFrame frame = new JFrame("Palette Frame");
                    frame.add(new PalettePanel());
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                }
                catch(Exception ex){
                    ex.printStackTrace();
                }
            }
        });
    }
}
class PalettePanel extends JPanel
{
    public PalettePanel(){
        ArrayList<Color> colors = new ArrayList<Color>();
        int[] values = {0,64,128,192,255};
        for(int red:values)for(int green:values)for(int blue:values)colors.add(new Color(red,green,blue));
        JPanel palette = new JPanel(new GridLayout(5,25,2,2));
        for(Color color:colors)palette.add(new ColoredButton(color));
        add(palette);
    }
    private class ColoredButton extends JButton
    {
        public ColoredButton(Color background){
            setBackground(background);
            setBorder(new LineBorder(Color.BLACK));
            setContentAreaFilled(false);
            setMargin(new Insets(10,10,10,10));
            setOpaque(true);
        }
    }
}

And this is what i get :

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Comparison method violates its general contract!
        at java.util.TimSort.mergeLo(Unknown Source)
        at java.util.TimSort.mergeAt(Unknown Source)
        at java.util.TimSort.mergeCollapse(Unknown Source)
        at java.util.TimSort.sort(Unknown Source)
        at java.util.Arrays.sort(Unknown Source)
        at java.util.ArrayList.sort(Unknown Source)
        at java.util.Collections.sort(Unknown Source)
        at javax.swing.SortingFocusTraversalPolicy.enumerateAndSortCycle(Unknown Source)
        at javax.swing.SortingFocusTraversalPolicy.getFocusTraversalCycle(Unknown Source)
        at javax.swing.SortingFocusTraversalPolicy.getFirstComponent(Unknown Source)
        at javax.swing.LayoutFocusTraversalPolicy.getFirstComponent(Unknown Source)
        at javax.swing.SortingFocusTraversalPolicy.getDefaultComponent(Unknown Source)
        at java.awt.FocusTraversalPolicy.getInitialComponent(Unknown Source)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
        at java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
        at java.awt.EventQueue.access$500(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.awt.EventQueue$4.run(Unknown Source)
        at java.awt.EventQueue$4.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.SequencedEvent.dispatch(Unknown Source)
        at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
        at java.awt.EventQueue.access$500(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.awt.EventQueue$4.run(Unknown Source)
        at java.awt.EventQueue$4.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)

Thanks for any help !!

[EDIT]

First of all,thanks for all your comments!

I just want to post a small update to my code, with those small changes i don't get any exception, maybe it could help someone with the same problem...

If i replace ColoredButton previous constructor with this one :

public ColoredButton(Color background){
            setBackground(background);
            setBorder(new CompoundBorder(new LineBorder(Color.BLACK),new EmptyBorder(5,5,5,5)));
            setContentAreaFilled(false);
            setOpaque(true);
        }

it works fine for me :)