As in the comments, there’s no default editor set - strange - $EDITOR env variable is empty. You can login into container with:
docker exec -it <container> bash
apt-get update apt-get install vim
or use the following Dockerfile:
FROM confluent/postgres-bw:0.1 RUN ["apt-get", "update"] RUN ["apt-get", "install", "-y", "vim"] EDIT
Docker images are delivered trimmed to bare minimum - so no editor is installed with the shipped container. That’s why there’s a need to install it manually.