src/JsonldServiceProvider.php
public function alter(ContainerBuilder $container) {

    if ($container->has('http_middleware.negotiation') && is_a(
        $container->getDefinition('http_middleware.negotiation')
          ->getClass(), '\Drupal\Core\StackMiddleware\NegotiationMiddleware', TRUE
    )
    ) {
      $container->getDefinition('http_middleware.negotiation')
        ->addMethodCall('registerFormat', ['jsonld', ['application/ld+json']]);
    }
  }
public function alter(ContainerBuilder $container) {

    if ($container->has('http_middleware.negotiation') && is_a(
        $container->getDefinition('http_middleware.negotiation')
          ->getClass(), '\Drupal\Core\StackMiddleware\NegotiationMiddleware', TRUE
    )
    ) {
      $container->getDefinition('http_middleware.negotiation')
        ->addMethodCall('registerFormat', ['jsonld', ['application/ld+json']]);
    }
  }
{@inheritdoc}