docs: public static boolean isSameDay(Calendar cal1, Calendar cal2) {
  		if (cal1 == null || cal2 == null) {
  			throw new IllegalArgumentException("The date must not be null");
  		}
  		return cal1.get(Calendar.DAY_OF_YEAR) == cal2.get(Calendar.DAY_OF_YEAR) && //
  				cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR) && //
  				cal1.get(Calendar.ERA) == cal2.get(Calendar.ERA);
  	}