Platform: ALL
JDK: 6, 7

The following code illustrates the problem

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import javax.swing.*;

public class MetalGetBaseLine {
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(
                new javax.swing.plaf.metal.MetalLookAndFeel());
        } catch (UnsupportedLookAndFeelException e) {
            e.printStackTrace();
        }
        new JComboBox().getBaseline(1, 3);
    }
}
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Ouput will be

Exception in thread "main" java.lang.IllegalArgumentException: Width and height must be >= 0
at javax.swing.plaf.ComponentUI.getBaseline(ComponentUI.java:292)
at javax.swing.plaf.basic.BasicComboBoxUI.getBaseline(BasicComboBoxUI.java:952)
at javax.swing.plaf.metal.MetalComboBoxUI.getBaseline(MetalComboBoxUI.java:149)
at javax.swing.JComponent.getBaseline(JComponent.java:2560)
at MetalGetBaseLine.main(MetalGetBaseLine.java:10)