code: public boolean isValid(String fodselsnummer, ConstraintValidatorContext constraintValidatorContext) {
          if(fodselsnummer == null){
              return true;
          }
  
          return isValid(fodselsnummer);
      }
docs: Validation method used by a JSR303 validator. Normally it is better to call the static methods directly.
  
  @param fodselsnummer
  The fodselsnummer to be validated
  @param constraintValidatorContext
  context sent in by a validator
  @return boolean
  whether or not the given fodselsnummer is valid