core:NPE when attempting to delete Everyone...

NPE when attempting to delete Everyone group from API

This patch addresses an NPE thrown when trying to delete the Everyone
group from the API. This exceptions cause the detail field to be skipped
in the respond.

Change-Id: Ic1faf6f97713f6adfce701126617b0463c118ce4
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1060528
Signed-off-by: Eli Mesika <emesika@redhat.com>