docs: @Nonnull
    public static IHolidayType getType (@Nonnull final HolidayType eType)
    {
      switch (eType)
      {
        case OFFICIAL_HOLIDAY:
          return EHolidayType.OFFICIAL_HOLIDAY;
        case UNOFFICIAL_HOLIDAY:
          return EHolidayType.UNOFFICIAL_HOLIDAY;
        default:
          throw new IllegalArgumentException ("Unknown type " + eType);
      }
    }