Method javax.swing.JLayer.remove(Component) doesn't follow general Swing practice and throw NPE for passed null arg in certain conditions. Please see the following sample:

import javax.swing.*;
import javax.swing.plaf.LayerUI;
import java.awt.*;

public class NPE {
    public static void main(String[] args) {
        JLayer<Button> layer = new JLayer<Button>(new Button());
        layer.setGlassPane(new JPanel());
        layer.setUI(new LayerUI<Button>() { });
        layer.remove((Component)null);
    }
}

Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.remove(Container.java:1228)
at javax.swing.JLayer.remove(JLayer.java:279)