Fixes #3417201: The callbacks must be serializable.

Closes #3417201

src/Auditor/AuditFilesManagedNotUsed.php

@@ -31,9 +31,6 @@ final class AuditFilesManagedNotUsed implements AuditFilesAuditorInterface {
   ) {
   }
 
-  /**
-   * {@inheritdoc}
-   */
   public function getReferences(): \Generator {
     $scheme = $this->auditFilesConfig->getFileSystemPath();
     $fu_query = $this->connection->select('file_usage', 'fu')->fields('fu', ['fid'])->execute()->fetchCol();
@@ -41,7 +38,7 @@ final class AuditFilesManagedNotUsed implements AuditFilesAuditorInterface {
       ->fields('fm', ['fid'])
       ->condition('fm.uri', $scheme . '://%', 'LIKE');
 
-    if (count($fu_query) > 0) {
+    if (\count($fu_query) > 0) {
       $query->condition('fm.fid', $fu_query, 'NOT IN');
     }