Comment 4 for bug 1331246

As for #1's 3
From discussion context, it should described as multi-attach status (may be 2-items?) not non-attach status (null).

Ref.
 Cinder/blueprints/multi-attach-volume
  https://wiki.openstack.org/wiki/Cinder/blueprints/multi-attach-volume
 Add volume multi attach support
  https://github.com/openstack/cinder/commit/10d54216871fde27172fbcb1a3c9bfec59b824c2