docs: private Relation<?> addNewRelation(SimpleTypeInformation<?> meta) {
      @SuppressWarnings("unchecked")
      SimpleTypeInformation<Object> ometa = (SimpleTypeInformation<Object>) meta;
      Relation<?> relation = new MaterializedRelation<>(ometa, ids);
      relations.add(relation);
      getHierarchy().add(this, relation);
      // Try to add indexes where appropriate
      for(IndexFactory<?> factory : indexFactories) {
        if(factory.getInputTypeRestriction().isAssignableFromType(meta)) {
          @SuppressWarnings("unchecked")
          final IndexFactory<Object> ofact = (IndexFactory<Object>) factory;
          @SuppressWarnings("unchecked")
          final Relation<Object> orep = (Relation<Object>) relation;
          Index index = ofact.instantiate(orep);
          index.initialize();
          getHierarchy().add(relation, index);
        }
      }
      return relation;
    }