Got this exception when a job is running. It appears everywhere in GUI where the build status is (status under the menu on the frontpage, executor status in configure, etc). I think it might be related to the plugin Gerrit trigger that adds information to the build status.
Got this exception on both Linux and Windows Jenkins server.
Downgraded to 1.502 (From 1.539) on the Windows Jenkins server and the problem seems to have disappeared. On the Linux server it appeared after a upgrade last week.