git clone https://github.com/k2nr/dokku-mysql-plugin.git mysql
chmod +x mysql/install mysql/commands
apt-get upgrade lxc-docker
sudo -sas a user with sudo privileges to log in as root.
I'm also getting the Unknown command: 'null' error even after upgrading docker and cloning the forked mysql plugin. I also tried the mariadb plugin, but that didn't work too well either. So far it seems like everything is changing too fast for all the plugins to keep up :(