code: public static HexString valueOf(String hex) {
  		return (hex == null || hex.equals("")) ? NULL : createHexString(hex);
  	}
docs: Create a new <code>HexString</code> instance from the given hexadecimal string.
  If <code>null</code> or an empty string is passed, will return a <code>HexString</code> instance
  with empty hex value and zero-length byte array.
  
  @param hex The hexadecimal string
  @return Immutable <code>HexString</code> instance encapsulating the hexadecimal string
  @throws IllegalArgumentException if malformed hex string (invalid or odd number of characters) is passed