api/keyupdater: invalid memory address during unit test

[Seman]

Invalid memory address or nil pointer dereference during github.com/juju/juju/api/keyupdater unit test:
http://reports.vapour.ws/releases/issue/57eacb31749a5646c50f38f9

ok github.com/juju/juju/api/keymanager 19.261s
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x20 pc=0xb35cb0]

goroutine 538 [running]:
panic(0x193e1a0, 0x482000e0f0)
 /usr/lib/go-1.6/src/runtime/panic.go:481 +0x384
gopkg.in/mgo%2ev2.logf(0x1f54380, 0x3a, 0x0, 0x0, 0x0)
 /home/ubuntu/juju-core_2.0-rc2/src/gopkg.in/mgo.v2/log.go:101 +0x90
gopkg.in/mgo%2ev2.(*mongoCluster).syncServersIteration(0x48203c4d00, 0x0)
 /home/ubuntu/juju-core_2.0-rc2/src/gopkg.in/mgo.v2/cluster.go:550 +0x40c
gopkg.in/mgo%2ev2.(*mongoCluster).syncServersLoop(0x48203c4d00)
 /home/ubuntu/juju-core_2.0-rc2/src/gopkg.in/mgo.v2/cluster.go:355 +0x1c8
created by gopkg.in/mgo%2ev2.newCluster
 /home/ubuntu/juju-core_2.0-rc2/src/gopkg.in/mgo.v2/cluster.go:78 +0x1e4
FAIL github.com/juju/juju/api/keyupdater 8.055s