I've added Dockerless instructions and the traceback to the readme. I Dockerized the example to make it entirely self-contained and reproducible, but I didn't realize I was making it harder to access. Sorry about that. And yes, registering the family in the script is my workaround, but I figured this was worth reporting anyway.

The Dockerfile changes the directory structure with the line COPY cfg/* /app/. I originally wanted to keep the config files in their own folder, but the simplest solution turned out to be moving them to the working directory. I realize now that it's confusing to change the directory structure in the Dockerfile. I've updated the repository; it should be clearer now.