Why can't I use the module keyword in Integration Service?

[MAXIANH0NG]

types:
idls:
- >
module dddds {
module msg{
struct a{
uint32 gait;
};

                struct b: MetaType {
                    GaitValue data;
                };
            };
            };

systems:
dds: { type: fastdds }
# ros1: { type: ros1 }
# ros2: { type: ros2 }
websocket: { type: websocket_server, security: none, port: 80 }

routes:
dds_server:
server: dds
# clients: [ros1, ros2, websocket]
clients: [websocket]
services:
add_two_ints: {
request_type: a,
reply_type: a,
route: dds_server,
remap: {
dds: {
topic: rt/dr/dddds::msg::dds_::a_,
},

    }
}

[Integration Service][WARN] [is::sh::FastDDS] Participant not provided in configuration file. A participant using the default transport locators and Domain ID 0 will be created.
[Integration Service][INFO] [is::sh::FastDDS::Participant] Created Fast DDS participant 'default_IS-FastDDS-SH_participant' with default QoS attributes and Domain ID: 0
[Integration Service][INFO] [is::sh::FastDDS] Configured!
[Integration Service][INFO] [is::sh::WebSocket::Server] Security disabled, creating TCP endpoint...
[Integration Service][INFO] [is::sh::WebSocket::Server] Initializing TCP server on port 80
[Integration Service][INFO] [is::sh::WebSocket::Server] Configured!
Segmentation fault (core dumped)