Error user_data must not be empty when not supplying user data.
$ tf plan
Error: module.swarm-cluster.module.managers.digitalocean_droplet.manager[0]: user_data must not be empty
Error: module.swarm-cluster.module.managers.digitalocean_droplet.manager[1]: user_data must not be empty
Error: module.swarm-cluster.module.managers.digitalocean_droplet.manager[2]: user_data must not be empty
Error
user_data must not be empty
when not supplying user data.