WordUtils.capitalize() can't handle 1:M conversions

// Failing test
assertEquals("SS", WordUtils.capitalize("\u00DF"));

public static String capitalize(final String str, final char... delimiters) {
    final int delimLen = delimiters == null ? -1 : delimiters.length;
    if (StringUtils.isEmpty(str) || delimLen == 0) {
        return str;
    }
    final StringBuffer buffer = new StringBuffer(str.length());
    final char[] chars = str.toCharArray();
    boolean capitalizeNext = true;
    for (int i = 0; i < chars.length; i++) {
        final char ch = chars[i];
        if (isDelimiter(ch, delimiters)) {
            capitalizeNext = true;
            buffer.append(ch);
        } else if (capitalizeNext) {
            // Use ENGLISH locale to be backwards compatible with previous releases, which
            // used Character.toUpperCase()
            buffer.append(String.valueOf(ch).toUpperCase(Locale.ENGLISH));
            capitalizeNext = false;
        } else {
            buffer.append(ch);
        }
    }
    return buffer.toString();
}