Delete FixityCheck entity if file entity doesn't exist

src/Entity/FixityCheck.php

@@ -208,7 +208,13 @@ class FixityCheck extends ContentEntityBase implements FixityCheckInterface {
   public function getFile(): ?File {
     /** @var \Drupal\Core\Field\EntityReferenceFieldItemList $file */
     $file = $this->file;
-    return $file->isEmpty() ? NULL : $file->referencedEntities()[0];
+
+    if ($file->isEmpty()) {
+      return NULL;
+    }
+
+    $referenced_entities = $file->referencedEntities();
+    return !empty($referenced_entities) ? reset($referenced_entities) : NULL;
   }
 
   /**

src/Plugin/QueueWorker/FixityCheckWorker.php

@@ -7,6 +7,7 @@ use Drupal\Core\Queue\QueueWorkerBase;
 use Drupal\dgi_fixity\FixityCheckServiceInterface;
 use Drupal\dgi_fixity\FixityCheckInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
+use function PHPUnit\Framework\isEmpty;
 
 /**
  * Performs a fixity check.
@@ -60,6 +61,10 @@ class FixityCheckWorker extends QueueWorkerBase implements ContainerFactoryPlugi
    */
   public function processItem($data) {
     if ($data instanceof FixityCheckInterface) {
+      if (isEmpty($data->getFile())) {
+        $data->delete();
+        return;
+      }
       /** @var \Drupal\dgi_fixity\FixityCheckInterface $data */
       $this->fixity->check($data->getFile());
     }