isValidNationalInsuranceNumber method
Checks the object is a String and is a valid UK national insurance number
Implementation
AbstractRuleBuilder isValidNationalInsuranceNumber({String? message}) {
return must((dynamic dyn) => dyn is String && CommonRegex.ninValidator.hasMatch(dyn), message ?? "String must be a valid national insurance number", code: "notValidNationalInsuranceNumber");
}