diff --git a/lib/datalib.php b/lib/datalib.php
index f4ba83205dd..8aa1f849a16 100644
--- a/lib/datalib.php
+++ b/lib/datalib.php
@@ -1662,6 +1662,8 @@ function add_to_log($courseid, $module, $action, $url='', $info='', $cm=0, $user
     $info = $info;
     if (!empty($url)) { // could break doing html_entity_decode on an empty var.
         $url = html_entity_decode($url);
+    } else {
+        $url = '';
     }
 
     // Restrict length of log lines to the space actually available in the