diff --git a/classes/local/store/object_file_system.php b/classes/local/store/object_file_system.php
index 86942af6..696af9cf 100644
--- a/classes/local/store/object_file_system.php
+++ b/classes/local/store/object_file_system.php
@@ -178,11 +178,13 @@ protected function get_mimetype_from_hash(string $contenthash): string {
 
         // We limit 1 because multiple files can have the same contenthash.
         // However, they all have the same mimetype so it does not matter which one we query.
-        return $DB->get_field_sql('SELECT mimetype
+        $mimetype = $DB->get_field_sql('SELECT mimetype
                               FROM {files}
                              WHERE contenthash = :hash
                              LIMIT 1',
                         ['hash' => $contenthash]);
+                        
+        return $mimetype ?? '';                   
     }
 
     /**