This is a follow-up to https://github.com/jenkinsci/jenkins/pull/3240 , see these comments:

• https://github.com/jenkinsci/jenkins/pull/3240#discussion_r162063623
• https://github.com/jenkinsci/jenkins/pull/3240#discussion_r162063644

It would be nice to create a new getter method in AbstractCIBase and to mark it as @Restricted(NoExternalUse.class) so that it becomes a core-internal API. It would help to avoid weird-looking and potentially unsafe package-level casts