code: private function prepareDomain(RequestContext $context, array &$parameters, int &$referenceType): void
      {
          if (isset($parameters['_ssl'])) {
              $context->setScheme(true === $parameters['_ssl'] ? 'https' : 'http');
          }
  
          if (isset($parameters['_domain']) && '' !== $parameters['_domain']) {
              $this->addHostToContext($context, $parameters, $referenceType);
          }
  
          unset($parameters['_domain'], $parameters['_ssl']);
      }
docs: Forces the router to add the host if necessary.