stringList method
A comma-separated flag (e.g. --queues=emails,default) split and
trimmed into a list, or null if the flag wasn't given.
Implementation
List<String>? stringList(String key) {
final raw = _values[key];
if (raw == null) return null;
return raw
.split(',')
.map((s) => s.trim())
.where((s) => s.isNotEmpty)
.toList();
}