@rastadrian You are right. Hence there is are some differences between automatically declining a PR with a bad code and preventing the merge of a bad code on the end of the day the result is the same, so the StashNotifier will do.
+1 with the notifier I don't see the need for jenkins to approve the PR on success. It wouldn't be hard to add as a feature if you really wanted the Jenkins approval. But as @rastadrian points out the notifier with the successful builds requirement in stash is good enough.