When writing rabl it is very easy to return AR objects instead of simple data structures in rabl:

http://projects.theforeman.org/issues/8774
http://projects.theforeman.org/issues/6215

in development this works fine since the OJ gem is loaded. In production this will fail and is difficult to debug since it does not occur in development. We should try to remove the Oj gem for better parity between dev and prod

Quoting dom:

                  │09:02:02         Dominic | should be possible to remove it, I think we added it for some new test in the auth system