certbot_create_extra_args not defined error

[boosh]

Looks like it needs a default value to stop ansible failing.

fatal: [web1]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: ... 'certbot_create_extra_args' is undefined\n\nThe error appears to be in '/Users/ansible/roles/geerlingguy.certbot/tasks/create-cert-standalone.yml': line 40, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: Generate new certificate if one doesn't exist.\n  ^ here\n"}