// Field validation
    // ----------------------------------------------------------------------

    /**
     * Asserts:
     * <p/>
     * <ul>
     * <li><code>string.length == null</code>
     * <li><code>string.length == 0</code>
     * </ul>
     */
    private static boolean validateStringEmpty(
            List<BuilderProblem> problems, String fieldName, String string, String message) {