code: private static String format(@Nullable final Pattern pattern) {
  		return String.format(DEFAULT_MESSAGE, patternToString(pattern));
  	}
docs: Returns the formatted string {@link IllegalPatternArgumentException#DEFAULT_MESSAGE} with the given pattern which
  the argument must match.
  
  @param argumentName
  the name of the passed argument
  @param pattern
  Pattern, that a string or character sequence should correspond to
  @return a formatted string of message with the given argument name