Use nullable typing (#6084)

app/Http/Middleware/Authenticate.php

@@ -10,7 +10,7 @@ class Authenticate extends Middleware
     /**
      * Get the path the user should be redirected to when they are not authenticated.
      */
-    protected function redirectTo(Request $request): string|null
+    protected function redirectTo(Request $request): ?string
     {
         return $request->expectsJson() ? null : route('login');
     }