code: public String toCuaPriority() {
  		if (value == null || value < 1 || value > 9) {
  			return null;
  		}
  		int letter = ((value - 1) / 3) + 'A';
  		int number = ((value - 1) % 3) + 1;
  		return (char) letter + "" + number;
  	}
docs: Converts this priority to its two-character CUA code.
  @return the CUA code (e.g. "B1" for "4") or null if the priority cannot
  be converted to a CUA code