API Improve type safety for Controller::join_links() (#11426)

Author: GuySartorelli

src/Control/Controller.php

@@ -627,9 +627,8 @@ public function redirectedTo()
      * Caution: All parameters are expected to be URI-encoded already.
      *
      * @param string|array $arg One or more link segments, or list of link segments as an array
-     * @return string
      */
-    public static function join_links($arg = null)
+    public static function join_links($arg = null): string
     {
         if (func_num_args() === 1 && is_array($arg)) {
             $args = $arg;