deploying a service to a space which has no subnets causes the agent to panic

To reproduce ensure you're using 1.25.

$ git rev-parse HEAD
aae914bdaf6cef2c177ae205c8087e53913d036d

$ juju version
1.25-beta1-trusty-amd64

# bootstrap on EC2
$ juju bootstrap -e amazon --upload-tools
Bootstrapping environment "amazon"
Starting new instance for initial state server
Launching instance
 - i-48044c9d
Building tools to upload (1.25-beta1.1-trusty-amd64)
Installing Juju agent on bootstrap instance
Waiting for address
Attempting to connect to 54.87.45.238:22
Attempting to connect to 10.230.166.135:22
Logging to /var/log/cloud-init-output.log on remote host
Installing package: curl
Installing package: cpu-checker
Installing package: bridge-utils
Installing package: rsyslog-gnutls
Installing package: cloud-utils
Installing package: cloud-image-utils
Installing package: tmux
Bootstrapping Juju machine agent
Starting Juju machine agent (jujud-machine-0)
Bootstrap agent installed
WARNING expected one instance, got 2
Waiting for API to become available
Bootstrap complete

$ juju status
environment: amazon
machines:
  "0":
    agent-state: started
    agent-version: 1.25-beta1.1
    dns-name: 54.87.45.238
    instance-id: i-48044c9d
    instance-state: running
    series: trusty
    hardware: arch=amd64 cpu-cores=1 cpu-power=100 mem=1740M root-disk=8192M availability-zone=us-east-1c
    state-server-member-status: has-vote
services: {}

# Create some spaces - note deliberately not adding any subnets.

$ juju space create public
created space "public" with no subnets

$ juju space create dmz
created space "dmz" with no subnets

# Now deploy ubuntu using a space constraint:
$ juju deploy ubuntu --constraints spaces=dmz

this will never complete because the agent panics, gets restarted, panics, ...

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x50 pc=0xa08a68]

goroutine 508 [running]:
runtime.panic(0x1a38200, 0x45355c8)
 /usr/lib/go/src/pkg/runtime/panic.c:266 +0xb6
github.com/juju/juju/provider/ec2.(*environ).StartInstance(0xc2101d8e10, 0x0, 0x0, 0x0, 0x0, ...)
 /home/aim/go/src/github.com/juju/juju/provider/ec2/environ.go:620 +0x16a8
github.com/juju/juju/worker/provisioner.(*provisionerTask).startMachine(0xc210494000, 0xc212039000, 0xc210cdc5b0, 0x0, 0x0, ...)
 /home/aim/go/src/github.com/juju/juju/worker/provisioner/provisioner_task.go:684 +0x5d
github.com/juju/juju/worker/provisioner.(*provisionerTask).startMachines(0xc210494000, 0xc2113fe778, 0x1, 0x1, 0x0, ...)
 /home/aim/go/src/github.com/juju/juju/worker/provisioner/provisioner_task.go:631 +0x3d7
github.com/juju/juju/worker/provisioner.(*provisionerTask).processMachines(0xc210494000, 0xc21099ba80, 0x1, 0x4, 0x1, ...)
 /home/aim/go/src/github.com/juju/juju/worker/provisioner/provisioner_task.go:293 +0xb62
github.com/juju/juju/worker/provisioner.(*provisionerTask).loop(0xc210494000, 0x0, 0x0)
 /home/aim/go/src/github.com/juju/juju/worker/provisioner/provisioner_task.go:165 +0x439
github.com/juju/juju/worker/provisioner.func·009()
 /home/aim/go/src/github.com/juju/juju/worker/provisioner/provisioner_task.go:90 +0x59
created by github.com/juju/juju/worker/provisioner.NewProvisionerTask
 /home/aim/go/src/github.com/juju/juju/worker/provisioner/provisioner_task.go:91 +0x1b5

(the rest of the stack trace is in the attached machine-0.log)