code: public long toMillis() {
  		long totalSeconds = 0;
  
  		if (weeks != null) {
  			totalSeconds += 60L * 60 * 24 * 7 * weeks;
  		}
  		if (days != null) {
  			totalSeconds += 60L * 60 * 24 * days;
  		}
  		if (hours != null) {
  			totalSeconds += 60L * 60 * hours;
  		}
  		if (minutes != null) {
  			totalSeconds += 60L * minutes;
  		}
  		if (seconds != null) {
  			totalSeconds += seconds;
  		}
  		if (prior) {
  			totalSeconds *= -1;
  		}
  
  		return totalSeconds * 1000;
  	}
docs: Converts the duration value to milliseconds.
  @return the duration value in milliseconds (will be negative if
  {@link #isPrior} is true)