The filter plugin 'valid_ip' failed: expected string or bytes-like object, got 'NoneType'

[dlucredativ]

Error while resolving value for 'cert_san': The filter plugin 'valid_ip' failed: expected string or bytes-like object, got 'NoneType'
Origin: /path/to/.ansible/roles/oxlorg.certs/tasks/snakeoil.yml:13:15

11 - name: Certificates | Snakeoil | Setting SAN
12   ansible.builtin.set_fact:
13     cert_san: "{% for domain in CERT_CONFIG.cert.domains %}
                 ^ column 15

fatal: [1.2.3.4]: FAILED! => {"changed": false, "msg": "Task failed: Finalization of task args for 'ansible.builtin.set_fact' failed: Error while resolving value for 'cert_san': The filter plugin 'valid_ip' failed: expected string or bytes-like object, got 'NoneType'"}

One has to set pmg.nginx.ip to something, which shouldn't be necessary.