code: public void addRepository(String id, URL url) {
          for (UpdateRepository ur : repositories) {
              if (ur.getId().equals(id)) {
                  throw new RuntimeException("Repository with id " + id + " already exists");
              }
          }
          repositories.add(new DefaultUpdateRepository(id, url));
      }
docs: Add one {@link DefaultUpdateRepository).
  
  @param id of repo
  @param url of repo