When adding a Build Other Projects step in the promotion process in a Job Template, the server raises a NullPointerException when processing the following request:

http://localhost:8083/job/test-job/descriptorByName/hudson.tasks.BuildTrigger/check?value=

The method doCheck in the BuildTrigger assume that the @AncestorInPath is not null which is a bug.

Source code is here: https://github.com/jenkinsci/jenkins/blob/e2dccc35572b64f5e602a6b1b3efb517c578872c/core/src/main/java/hudson/tasks/BuildTrigger.java#L371

How to reproduce:

• Create a Job Template "test-job" at the root
• Tick "Define Promotion Process"
• "Build Other Projects" action
• An ERROR link appears

Note: This issue does not block the functionality and this error can be ignored. Specifying an existing project and saving the configuration will make this error disappears.