Cannot run pipeline manually with except changes

Summary

If .gitlab-ci.yml contains execpt:changes, the pipeline cannot be run manually. The following error is received:

The form contains the following error:
No stages / jobs for this pipeline.

see forum discussion https://forum.gitlab.com/t/run-pipeline-manually-with-except-changes/23234

Steps to reproduce

• edit .gitlab-ci.yml removing README exception
• commit
• pipeline triggered by commit
• pipeline can be manually triggered
• edit .gitlab-ci.yml adding README exception
• commit
• pipeline triggered by commit
• pipeline cannot be manually triggered, above error displayed
• rinse and repeat

Example Project

.gitlab-ci.yml

job:
  image: ubuntu:xenial
  script:
  - echo "Sup?"
  except:
    changes:
    - README.md

Documentation Update

Part of the fix here should be to update the documentation for only/except to mention that rules offers a more powerful syntax.