Fix null handling in LoginLinkRequest userAttributes

Previously, the method could return `null` if `user_attributes` was not set. This update ensures it always returns an array, preventing potential issues with downstream usage.

src/Http/Requests/LoginLinkRequest.php

@@ -19,6 +19,10 @@ public function rules(): array
 
     public function userAttributes(): array
     {
-        return json_decode($this->user_attributes, true) ?? [];
+        if ($this->user_attributes !== null) {
+            return json_decode($this->user_attributes);
+        }
+
+        return [];
     }
 }