docs: fix PHPDoc types in Common

Author: kenjis

system/Common.php

@@ -823,10 +823,10 @@ function model(string $name, bool $getShared = true, ?ConnectionInterface &$conn
      * Provides access to "old input" that was set in the session
      * during a redirect()->withInput().
      *
-     * @param null        $default
+     * @param string|null $default
      * @param bool|string $escape
      *
-     * @return mixed|null
+     * @return array|string|null
      */
     function old(string $key, $default = null, $escape = 'html')
     {
@@ -932,7 +932,7 @@ function route_to(string $method, ...$params)
      *
      * @param string $val
      *
-     * @return mixed|Session|null
+     * @return array|bool|float|int|object|Session|string|null
      */
     function session(?string $val = null)
     {