Merge pull request #3462 from tsl0922/fix-reassign-error

fix: wrong number of arguments

app/observers/merge_request_observer.rb

@@ -20,6 +20,6 @@ class MergeRequestObserver < BaseObserver
   end
 
   def after_update(merge_request)
-    notification.reassigned_merge_request(merge_request) if merge_request.is_being_reassigned?
+    notification.reassigned_merge_request(merge_request, current_user) if merge_request.is_being_reassigned?
   end
 end