@Nullable
  static ServiceViewContributor getTheOnlyRootContributor(List<? extends ServiceViewItem> items) {
    ServiceViewContributor result = null;
    for (ServiceViewItem node : items) {
      if (result == null) {
        result = node.getRootContributor();
      }
      else if (result != node.getRootContributor()) {
        return null;
      }
    }
    return result;
  }
@Nullable
  static ServiceViewContributor getTheOnlyRootContributor(List<? extends ServiceViewItem> items)