When you try and view the XML api for a multibarnch pipeline job you are greated with an angry jenkins when you export depth > 1.

org.kohsuke.stapler.export.NotExportableException: class jenkins.scm.api.SCMHeadOrigin$Fork doesn't have @ExportedBean

 
org.kohsuke.stapler.export.NotExportableException: class jenkins.scm.api.SCMHeadOrigin$Default doesn't have @ExportedBean

The default is exported at least here presumably there are other exports from implementations of the branch-source.

To reproduce

Create a MultiBranch pipeline from a GitHub repo.

Make sure you have a PR, and some branches

go to ${joburl}/job/${branch}/api/xml?depth=3   

or ${joburl}/view/change-requests/job/${PR-number}/api/xml?depth=3

sit back and enjoy