The IssueNotifier has started throwing exceptions today. Here is a description of the situation:

1. The jdk17 repo was tagged with jdk-17+28
2. The commit with that tag was included in the forward merge to the jdk repo
3. The PR for the forward merge created a pr/XXXX branch in the jdk repo
4. The PR has not yet been merged

Because of 3, the tagged commit, and so the tag, was added to the jdk repo before the PR was actually merged. The notifier finds this new tag and starts notifying. The IssueNotifier needs to find what branch the tag is present in to figure out the fixVersion and backport to update. While doing this, if it ends up not finding any branch (except for pr/X branches), it throws an exception. By throwing an exception, we end up in a loop as the bot will just retry endlessly.

Taking a step back, I noticed that the MailingListNotifier succeeded with this notification, and sent out an email about this new tag entering the mainline jdk repo. This email was sent out prematurely since the tag is still just in the pr branch: https://mail.openjdk.java.net/pipermail/jdk-changes/2021-June/014126.html

My conclusion is that when reacting to tags, we need to filter them and ignore tags that are only present in pr branches.