fix: sid generation in cookie middleware (compwright#5)

Co-authored-by: Yani <[email protected]>

Author: yani

src/Middleware/SessionCookieMiddleware.php

@@ -27,7 +27,7 @@ public function process(
 
         // Read the session cookie
         $cookies = $request->getCookieParams();
-        $sid = $cookies[$manager->name()] ?? '';
+        $sid = $cookies[$manager->name()] ?? null;
         $manager->id($sid);
 
         // Handle the request