copyWith method
Implementation
Contact copyWith({
  String? phoneNumber,
  String? firstName,
  String? lastName,
  String? vcard,
  int? userId,
}) => Contact(
  phoneNumber: phoneNumber ?? this.phoneNumber,
  firstName: firstName ?? this.firstName,
  lastName: lastName ?? this.lastName,
  vcard: vcard ?? this.vcard,
  userId: userId ?? this.userId,
);