I believe this was ultimately caused by the lack of an explicit subscription, which was addressed by https://bugzilla.redhat.com/show_bug.cgi?id=1370218. We can add a .to_s guard here, but once the hotfix was applied, this error went away.
I also added a guard here: https://github.com/ManageIQ/manageiq/pull/10846
Reviewed code. Developer verified the fix worked when applied to his account. Moving to verified.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://rhn.redhat.com/errata/RHSA-2016-1996.html