This code was added to address JENKINS-39107. We have a use-case where our jobs use lightweight checkout to load build scripts from gitlab, but the Jenkinsfiles themselves checkout from p4 to get the actual code that we build.
The added code then tries to run 'p4 where' on the Jenkinsfile, but it doesn't exist in p4. This doesn't cause any build failures, but does print the following message:
which causes our failure tracking to erroneously pick it up (because it's a legitimate failure at times in other cases).