validateholder method
Implementation
String? validateholder(String value) {
if (value.isEmpty) return "Enter Card Holder Name";
// Pattern pattern =
// r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{6,}$';
// RegExp regex = RegExp(pattern);
// if (!regex.hasMatch(value.trim())) {
// return "include one capital letter, number and symbol";
// }
return null;
}