docs: public ResourceList getResourceList() {
          final Set<ResourceActivity> resourceActivities = getResourceActivities();
          final List<ResourceList> resourceLists = new ArrayList<ResourceList>(1 + resourceActivities.size());
          for (ResourceActivity activity : resourceActivities) {
              if (activity != this && activity != null) {
                  // defensive infinite recursion and null check
                  resourceLists.add(activity.getResourceList());
              }
          }
          return ResourceList.union(resourceLists);
      }