We use "jenkins-cli.jar set-build-description" command for integration with external CI systems - they record build number, do their processing, then post status back to jenkins by updating build description. Sometimes, recorded build number no longer exists (e.g. was expired), and in thsi case, set-build-description command fails with NullPointerException (and exist code of 255). Of course, NPE isn't selective enough to differentiate "build doesn't exist" (warning-like condition) from more serious error which may require closer attention.
It would be nice if set-build-description checked build existence, and exited with specific error message and specific exit code for easy scripting.