docs: @Nonnegative
    public static DayOfWeek getWeekday (@Nonnull final Weekday eWeekday)
    {
      switch (eWeekday)
      {
        case MONDAY:
          return DayOfWeek.MONDAY;
        case TUESDAY:
          return DayOfWeek.TUESDAY;
        case WEDNESDAY:
          return DayOfWeek.WEDNESDAY;
        case THURSDAY:
          return DayOfWeek.THURSDAY;
        case FRIDAY:
          return DayOfWeek.FRIDAY;
        case SATURDAY:
          return DayOfWeek.SATURDAY;
        case SUNDAY:
          return DayOfWeek.SUNDAY;
        default:
          throw new IllegalArgumentException ("Unknown weekday " + eWeekday);
      }
    }