  void addPayload(const std::string& name, const ProtobufWkt::Struct& payload) {
    *(*payload_.mutable_fields())[name].mutable_struct_value() = payload;
  }
  void addPayload(const std::string& name, const ProtobufWkt::Struct& payload) {
    *(*payload_.mutable_fields())[name].mutable_struct_value() = payload;
  }