docs: @Nonnull
    private static CalendarHierarchy _createConfigurationHierarchy (@Nonnull final Configuration aConfig,
                                                                    @Nullable final CalendarHierarchy aParent)
    {
      final ECountry eCountry = ECountry.getFromIDOrNull (aConfig.getHierarchy ());
      final CalendarHierarchy aHierarchy = new CalendarHierarchy (aParent, aConfig.getHierarchy (), eCountry);
      for (final Configuration aSubConfig : aConfig.getSubConfigurations ())
      {
        final CalendarHierarchy aSubHierarchy = _createConfigurationHierarchy (aSubConfig, aHierarchy);
        aHierarchy.addChild (aSubHierarchy);
      }
      return aHierarchy;
    }