diff --git a/src/Observers/NovaInlineRelationshipObserver.php b/src/Observers/NovaInlineRelationshipObserver.php
index 606a7ba..a0451f6 100644
--- a/src/Observers/NovaInlineRelationshipObserver.php
+++ b/src/Observers/NovaInlineRelationshipObserver.php
@@ -80,7 +80,7 @@ public function callEvent(Model $model, string $event)
      *
      * @return RelationshipObservable
      */
-    public function getRelationshipObserver(Model $model, $relationship): RelationshipObservable
+    public function getRelationshipObserver(Model $model, $relationship): ?RelationshipObservable
     {
         $className = NovaInlineRelationshipHelper::getObserver($model->{$relationship}());