code: protected function fillFromCustomer(ContextInterface $context, CustomerInterface $customer): void
      {
          if (null === $context->getCustomerGroup()) {
              $context->setCustomerGroup($customer->getCustomerGroup());
          }
          if (null === $context->getInvoiceCountry()) {
              if (null !== $address = $customer->getDefaultInvoiceAddress(true)) {
                  $context->setInvoiceCountry($address->getCountry());
              }
          }
          if (null === $context->getDeliveryCountry()) {
              if (null !== $address = $customer->getDefaultDeliveryAddress(true)) {
                  $context->setDeliveryCountry($address->getCountry());
              }
          }
          /*if (null === $context->getCurrency()) {
              $context->setCurrency($customer->getCurrency());
          }
          if (null === $context->getLocale()) {
              $context->setLocale($customer->getLocale());
          }*/
      }
docs: Fills the context from the given customer.
  
  @param ContextInterface  $context
  @param CustomerInterface $customer