JLayer.isOptimizedDrawingEnabled() throws NPE for null glass pane set

Method javax.swingJLayer.isOptimizedDrawingEnabled() throws NPE if glass pane is set to null.

Please see the following code sample:

public class NPE {
    public static void main(String[] args) {
        javax.swing.JLayer layer = new javax.swing.JLayer();
        layer.setGlassPane(null);
        layer.isOptimizedDrawingEnabled();
    }
}

Exception in thread "main" java.lang.NullPointerException
at javax.swing.JLayer.isOptimizedDrawingEnabled(JLayer.java:322)
...
The following JCK test fails due to this problem
api/javax_swing/JLayer/index.html#General[isOptimizedDrawingEnabled_nullGlassPane]