[FIXED JENKINS-38721, JENKINS-37282] - NPE in "CauseOfInterruption.UserInterruption" when user is missing (#2630)

* [FIXED JENKINS-38721] - Prevent NPE during rendering of "CauseOfInterruption.UserInterruption" when user is missing

It is a regression introduced in JENKINS-36594

* [JENKINS-38721] - Fix typo

(cherry picked from commit 91ad5921)