'juju-ha-spaces is not set' error on single node

[Matt Verran]

On single node install (--topology single) I receive the below error. Since this is a small install on a single system it makes no sense to enable_ha in juju...

machine-0: 14:25:56 ERROR juju.worker.dependency "peer-grouper" manifold worker returned unexpected error: computing desired peer group: updating member addresses: juju-ha-space is not set and these nodes have more than one usable address: 0
run "juju controller-config juju-ha-space=<name>" to set a space for Mongo peer communication
machine-0: 14:27:46 ERROR juju.worker.dependency "peer-grouper" manifold worker returned unexpected error: computing desired peer group: updating member addresses: juju-ha-space is not set and these nodes have more than one usable address: 0
run "juju controller-config juju-ha-space=<name>" to set a space for Mongo peer communication

Without really understanding this i've issued juju controller-config juju-ha-space=alpha to see what happens and the bootstrap does complete.