diff --git a/lib/weblib.php b/lib/weblib.php
index 10b27d82cda..45b00ef4e69 100644
--- a/lib/weblib.php
+++ b/lib/weblib.php
@@ -91,13 +91,18 @@ define('URL_MATCH_EXACT', 2);
  * @return string
  */
 function s($var) {
-
     if ($var === false) {
         return '0';
     }
 
-    return preg_replace('/&#(\d+|x[0-9a-f]+);/i', '&#$1;',
-            htmlspecialchars($var ?? '', ENT_QUOTES | ENT_HTML401 | ENT_SUBSTITUTE));
+    if ($var === null || $var === '') {
+        return '';
+    }
+
+    return preg_replace(
+        '/&#(\d+|x[0-9a-f]+);/i', '&#$1;',
+        htmlspecialchars($var, ENT_QUOTES | ENT_HTML401 | ENT_SUBSTITUTE)
+    );
 }
 
 /**