docs: public static String toUpperCase(String dn) {
          if (dn == null)
              return null;
  
          String newDN = null;
          if (dn.indexOf('\u00df') != -1) {
              // convert each character in DN to upper case except '?'(\u00df)
              char[] chars = new char[dn.length()];
              for (int index = 0; index < dn.length(); index++) {
                  char c = dn.charAt(index);
                  if (c == '\u00df') {
                      chars[index] = c;
                  } else {
                      chars[index] = Character.toUpperCase(c);
                  }
              }
              newDN = new String(chars);
          } else {
              newDN = dn.toUpperCase();
          }
          return newDN;
      }