LIST_CASE(tensor, TF_ATTR_FUNC);
#undef LIST_CASE
      // All lists empty, determine the type from the OpDef.
      if (metadata.list_size == 0) {
        for (int i = 0; i < oper->node.op_def().attr_size(); ++i) {
          const auto& a = oper->node.op_def().attr(i);
          if (a.name() != attr_name) continue;
          const string& typestr = a.type();
          if (typestr == "list(string)") {