public static ClassDoc getFirstVisibleSuperClassCD(ClassDoc classDoc,
            Configuration configuration) {
        if (classDoc == null) {
            return null;
        }
        ClassDoc supClassDoc = classDoc.superclass();
        while (supClassDoc != null &&
                  (! (supClassDoc.isPublic() ||
                              isLinkable(supClassDoc, configuration))) ) {
            supClassDoc = supClassDoc.superclass();
        }
        if (classDoc.equals(supClassDoc)) {
            return null;
        }
        return supClassDoc;
    }