code: protected static char[] flags(final String flagString) {
          if (flagString == null || flagString.isEmpty()) {
              return NO_FLAGS;
          }
          noDupsExcept(flagString, NO_FLAGS);
          final char[] flags = flagString.toCharArray();
          Arrays.sort(flags);
          return flags;
      }
docs: Converts a string of flags into a sorted flag array,
  that can be passed as a parameter to other utility methods.
  @param flagString
  @return sorted flag array