Fix Request locale property doc types

Author: bytestream

src/Symfony/Component/HttpFoundation/Request.php

@@ -191,7 +191,7 @@ class Request
     protected $session;
 
     /**
-     * @var string
+     * @var string|null
      */
     protected $locale;
 
@@ -1452,7 +1452,7 @@ public function setLocale(string $locale)
      */
     public function getLocale()
     {
-        return null === $this->locale ? $this->defaultLocale : $this->locale;
+        return $this->locale ?? $this->defaultLocale;
     }
 
     /**