code: public static Date atStartOfDay(Date date) {
      LocalDateTime localDateTime = dateToLocalDateTime(date);
      LocalDateTime startOfDay = localDateTime.with(LocalTime.MIN);
      return localDateTimeToDate(startOfDay);
    }
docs: Returns the {@link Date} of midnight at the start of the given {@link Date}.
  
  <p>This returns a {@link Date} formed from the given {@link Date} at the time of midnight,
  00:00, at the start of this {@link Date}.
  
  @return the {@link Date} of midnight at the start of the given {@link Date}