['link_class', '=', 'star'],
['head_uuid', 'is_a', 'arvados#group']]).with_count("none").select(%w(head_uuid))
uuids = links.collect { |x| x.head_uuid }
['link_class', '=', 'star'],
['head_uuid', 'is_a', 'arvados#group']]).with_count("none").select(%w(head_uuid))
uuids = links.collect { |x| x.head_uuid }