validateOneOfRequired function
Returns null if at least one of values is non-null and non-empty (for strings).
Implementation
String? validateOneOfRequired(List<Object?> values, {String fieldNames = _kDefaultFieldNames}) {
final bool hasAny = values.any(
(Object? v) {
if (v == null) return false;
if (v is String) return v.trim().isNotEmpty;
return true;
},
);
return hasAny ? null : 'At least one of $fieldNames is required';
}