code: protected function resolveCustomerTargetCountry(CustomerInterface $customer): ?CountryInterface
      {
          if (null !== $address = $customer->getDefaultDeliveryAddress()) {
              return $address->getCountry();
          }
  
          return null;
      }
docs: Resolves the customer's taxation target country.
  
  @param CustomerInterface $customer
  
  @return CountryInterface|null