diff --git a/_protected/framework/Url/Url.class.php b/_protected/framework/Url/Url.class.php
index edddc8df3e..5561afc10e 100755
--- a/_protected/framework/Url/Url.class.php
+++ b/_protected/framework/Url/Url.class.php
@@ -51,7 +51,7 @@ public static function clean(string $sUrl): string
      *
      * @return string Returns a URL-encoded string.
      */
-    public static function httpBuildQuery(array $aParams, string $sNumericPrefix = '', string $sArgSeparator = '&', int $iEncType = PHP_QUERY_RFC1738): string
+    public static function httpBuildQuery(array $aParams, string $sNumericPrefix = '', string|null $sArgSeparator = '&', int $iEncType = PHP_QUERY_RFC1738): string
     {
         return http_build_query($aParams, $sNumericPrefix, $sArgSeparator, $iEncType);
     }