loki_push_api does not like loki_alert_rules being an empty file.

[PietroPasotti]

_is_official_alert_rule_format(rule_file)
raises an uncaught TypeError: argument of type 'NoneType' is not iterable
when loki_alert_rules is an empty file.

Is that a valid 'rules' file to begin with?
Either way, looks like we should return list() in _from_file even if the file is invalid/empty.

[PietroPasotti]

note: underlying issue is that yaml.safe_load(stream) can and does return None in this case.

[Abuelodelanada]

Thanks for the report Pietro!