diff --git a/message_highlight.php b/message_highlight.php
index b49189a..1584cfd 100644
--- a/message_highlight.php
+++ b/message_highlight.php
@@ -49,7 +49,7 @@ public function init()
    */
   function storage_init($p)
   {
-    $p['fetch_headers'] .= trim($p['fetch_headers']. ' ' . 'CC');
+    $p['fetch_headers'] = trim(($p['fetch_headers'] ?? '') . ' ' . 'CC');
     return($p);
   }