minor #42490 More return type fixes (bis) (nicolas-grekas)

This PR was merged into the 5.4 branch.

Discussion
----------

More return type fixes (bis)

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Commits
-------

c6a20b4e4d More return type fixes (bis)

Author: nicolas-grekas

Request.php

@@ -939,7 +939,7 @@ public function getScheme()
      *
      * The "X-Forwarded-Port" header must contain the client port.
      *
-     * @return int|string can be a string if fetched from the server bag
+     * @return int|string|null Can be a string if fetched from the server bag
      */
     public function getPort()
     {

Session/Storage/MetadataBag.php

@@ -139,6 +139,7 @@ public function getLastUsed()
     public function clear()
     {
         // nothing to do
+        return null;
     }
 
     /**