Ros1_bridge for builtin interfaces results in an error

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My project is publishing in a ros2 node a duration msg and want to record it in a rosbag (ros1) (since there is no ros2 python rosbag api yet and want to do some python plotting, right ?).

I get following error from the ros1 bridge (command with the options are : ros2 run ros1_bridge dynamic_bridge --bridge-all-topics)

failed to create 2to1 bridge for topic '/........' with ROS 2 type 'builtin_interfaces/msg/Duration' and ROS 1 type '': No template specialization for the pair

I use melodic and dashing.

In the code I see a check on ros2_type_name == "builtin_interfaces/Duration" and not on ros2_type_name == "builtin_interfaces/msg/Duration". Could this be a bug or something I'm doing wrong ?