Merge pull request #288 from pajkho/patch-1

 Fix Call to a member function only() on null error

Author: musonza

src/Models/Message.php

@@ -48,6 +48,10 @@ public function getSenderAttribute()
     {
         $participantModel = $this->participation->messageable;
 
+        if (!isset($participantModel)) {
+            return null;
+        }
+
         if (method_exists($participantModel, 'getParticipantDetails')) {
             return $participantModel->getParticipantDetails();
         }