docs: public synchronized void load() throws IOException {
          XmlFile file = getConfigFile();
          if(file.exists()) {
              try {
                  sites.replaceBy(((PersistedList)file.unmarshal(sites)).toList());
              } catch (IOException e) {
                  LOGGER.log(Level.WARNING, "Failed to load "+file, e);
              }
              boolean defaultSiteExists = false;
              for (UpdateSite site : sites) {
                  // replace the legacy site with the new site
                  if (site.isLegacyDefault()) {
                      sites.remove(site);
                  } else if (ID_DEFAULT.equals(site.getId())) {
                      defaultSiteExists = true;
                  }
              }
              if (!defaultSiteExists) {
                  sites.add(createDefaultUpdateSite());
              }
          } else {
              if (sites.isEmpty()) {
                  // If there aren't already any UpdateSources, add the default one.
                  // to maintain compatibility with existing UpdateCenterConfiguration, create the default one as specified by UpdateCenterConfiguration
                  sites.add(createDefaultUpdateSite());
              }
          }
      }