validateOneOf function
Validates that exactly one value in the given list is not null.
Throws a Exception when no or more than one value is not null.
Implementation
void validateOneOf(List<dynamic> values, List<String> names) {
final match = values.singleWhereOrNull((x) => x != null);
if (match == null) {
throw Exception('Exactly one of $names must not be null: $values');
}
}