Only 'Make HTTP Request' if file present in repository?

I have Phabricator setup with a Herald rule triggering a Harbormaster build plan making an HTTP request to Jenkins. It is doing this even for old branches which are not setup for builds. I was attempting to avoid the pile of broken builds that are expected to fail by at some point in the Phabricator action chain stopping if the Jenkinsfile is not present in that branch. I checked Herald conditions for the commit-triggered rule and saw only the ability to set conditions for changed files, not simply existent files.

Is there a tidy way to avoid the broken builds from the Phabricator side? Or a reason this should be handled on the Jenkins side?

Thanks for any help.

Cheers,
-kyle

There is no way to do this in Phabricator, and there are currently no plans to add support.