diff --git a/core/src/Legacy/Cache.php b/core/src/Legacy/Cache.php
index d80e7bd44c..92dced3bd6 100644
--- a/core/src/Legacy/Cache.php
+++ b/core/src/Legacy/Cache.php
@@ -73,8 +73,7 @@ public function escapeDoubleQuotes($s)
     {
         $q1 = array("\\", "\"", "\r", "\n", "\$");
         $q2 = array("\\\\", "\\\"", "\\r", "\\n", "\\$");
-
-        return str_replace($q1, $q2, $s);
+        return str_replace($q1, $q2, ($s ?? ''));
     }
 
     /**