If I create the following Jenkins file in the pipeline editor:
Everything works fine. If I add the following snippet after the stage line:
Then the pipeline editor displays a blank page. If I remove the snipped then all is back normal in the editor.
This Jenkinsfile is the same as the Jenkinsfile in the https://github.com/jenkinsci/jenkins-test-harness-htmlunit/blob/master/Jenkinsfile repository which is utilized by the ci.jenkins.io build site.