diff --git a/src/PersistentData/Model/ModelWithSlug.php b/src/PersistentData/Model/ModelWithSlug.php
index e691f26..036bedb 100644
--- a/src/PersistentData/Model/ModelWithSlug.php
+++ b/src/PersistentData/Model/ModelWithSlug.php
@@ -18,7 +18,7 @@ abstract class ModelWithSlug extends Model
         $this->slug = $slug;
     }
 
-    public function getSlug(): string
+    public function getSlug(): ?string
     {
         return $this->slug;
     }