If you pass a service-hostname of (for instance) "None" to the charm, it will happily try to create an ingress named "None-ingress". This will fail as follows:
HTTP response body: {"kind":"Status","apiVersion":"v1","metadata":{},"status":"Failure","message":"Ingress.extensions \"None-ingress\" is invalid: [metadata.name: Invalid value: \"None-ingress\": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*'), spec.rules[0].host: Invalid value: \"None\": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')]","reason":"Invalid","details":{"name":"None-ingress","group":"extensions","kind":"Ingress","causes":[{"reason":"FieldValueInvalid","message":"Invalid value: \"None-ingress\": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')","field":"metadata.name"},{"reason":"FieldValueInvalid","message":"Invalid value: \"None\": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')","field":"spec.rules[0].host"}]},"code":422}
The charm should likely go into blocked state with a message, or an error state with a message explaining the problem.
This is now being tracked in https:/