getVirtualOrMissingResourceIdentifier example

  public static function toResourceIdentifier(EntityReferenceItem $item, $arity = NULL) {
    $property_name = static::getDataReferencePropertyName($item);
    $target = $item->get($property_name)->getValue();
    if ($target === NULL) {
      return static::getVirtualOrMissingResourceIdentifier($item);
    }
    assert($target instanceof EntityInterface);
    /** @var \Drupal\jsonapi\ResourceType\ResourceTypeRepositoryInterface $resource_type_repository */
    $resource_type_repository = \Drupal::service('jsonapi.resource_type.repository');
    $resource_type = $resource_type_repository->get($target->getEntityTypeId(), $target->bundle());
    // Remove unwanted properties from the meta value, usually 'entity'     // and 'target_id'.     $properties = TypedDataInternalPropertiesHelper::getNonInternalProperties($item);
    $main_property_name = $item->getDataDefinition()->getMainPropertyName();
    $meta = array_diff_key($properties, array_flip([$property_name, $main_property_name]));
    if (!is_null($arity)) {