Before anyone guns me down..I have looked at all the messages that has this error but they seem to manifest from a different problem,I couldn\'t get any substantial information.
Looks like you ran a Jenkins Gerrit Trigger build manually? The trigger page says,
Using "Build Now" [..] Add a String parameter called GERRIT_REFSPEC with the default value refs/heads/master
https://wiki.jenkins-ci.org/display/JENKINS/Gerrit+Trigger