When displaying the promotion status of a job with a once run, but now deleted promotion step, a NPE is written to the log, and a click on "Re-Execute promotion" yields a 404

Steps to reproduce

1. Configure a freestyle job "test-deleted-promotion", with a promotion step "Test1" with manual approval.
There's no build steps required in both the job and the promotion step.
2. Run the Job once, then run the promotion step once.
3. Go to the job's configure page and delete the promotion step.
4. Navigate to job/test-deleted-promotion/1/promotion
Jenkins writes the attached stacktrace to the log
5. Click on "Re-Execute promotion".
Jenkins responds with 404 not found