fallback to primary key if owner key doesnt exist on model at all

Author: taylorotwell

Eloquent/Relations/MorphTo.php

@@ -231,8 +231,14 @@ protected function matchToMorphParents($type, Collection $results)
      */
     public function associate($model)
     {
+        if ($model instanceof Model) {
+            $foreignKey = $this->ownerKey && $model->{$this->ownerKey}
+                            ? $this->ownerKey
+                            : $model->getKeyName();
+        }
+
         $this->parent->setAttribute(
-            $this->foreignKey, $model instanceof Model ? $model->{$this->ownerKey ?: $model->getKeyName()} : null
+            $this->foreignKey, $model instanceof Model ? $model->{$foreignKey} : null
         );
 
         $this->parent->setAttribute(