destroying a subordinate service after destroying its primary services results in a traceback...

[Clint Byrum]

Steps to reproduce:

(assuming bootstrapped precise)
export JUJU_REPOSITORY=/usr/share/doc/juju/examples
juju deploy local:mysql
juju deploy cs:~clint-fewbar/oneiric/munin-node
juju deploy munin
juju add-relation mysql munin-node
juju add-relation munin-node:munin munin
juju destroy-service mysql
juju destroy-service munin-node

Debug log will show the traceback and the old unit agent will be left running on the machine. Given the lack of cleanup I understand that the best way is to terminate the machine, but I'd like to see these agents at least get gracefully removed from the machine in case I just want to re-deploy the same thing to it.

juju:
  Installed: 0.5+bzr529-1juju5~precise1
  Candidate: 0.5+bzr529-1juju5~precise1
  Version table:
 *** 0.5+bzr529-1juju5~precise1 0
        500 http://ppa.launchpad.net/juju/pkgs/ubuntu/ precise/main amd64 Packages
        100 /var/lib/dpkg/status
     0.5+bzr504-0ubuntu1 0
        500 http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ precise/universe amd64 Packages

=== Traceback ===

2012-04-15 07:25:03,717 unit:munin-node/3: twisted ERROR: Unhandled error in Deferred:
2012-04-15 07:25:03,719 unit:munin-node/3: twisted ERROR: Unhandled Error
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 362, in callback
    self._startRunCallbacks(result)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 458, in _startRunCallbacks
    self._runCallbacks()
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 545, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1095, in gotResult
    _inlineCallbacks(r, g, deferred)
--- <exception caught here> ---
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1039, in _inlineCallbacks
    result = g.send(result)
  File "/usr/lib/python2.7/dist-packages/juju/state/base.py", line 139, in __topology_changed
    yield watch_topology_function(self._old_topology, new_topology)
  File "/usr/lib/python2.7/dist-packages/juju/state/service.py", line 564, in watch_topology
    self._internal_id)
  File "/usr/lib/python2.7/dist-packages/juju/state/topology.py", line 487, in get_relations_for_service
    self._assert_service(service_id)
  File "/usr/lib/python2.7/dist-packages/juju/state/topology.py", line 517, in _assert_service
    "Service not found: %s" % service_id)
juju.state.topology.InternalTopologyError: Service not found: service-0000000019

2012-04-15 07:25:03,952 unit:munin-node/3: juju.agents.unit DEBUG: Configuration Changed
2012-04-15 07:25:03,960 unit:munin-node/3: twisted ERROR: Unhandled error in Deferred:
2012-04-15 07:25:03,962 unit:munin-node/3: twisted ERROR: Unhandled Error
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 391, in errback
    self._startRunCallbacks(fail)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 458, in _startRunCallbacks
    self._runCallbacks()
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 545, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1095, in gotResult
    _inlineCallbacks(r, g, deferred)
--- <exception caught here> ---
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1037, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python2.7/dist-packages/twisted/python/failure.py", line 382, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "/usr/lib/python2.7/dist-packages/juju/state/service.py", line 598, in watcher
    yield callback(change_event)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1037, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python2.7/dist-packages/twisted/python/failure.py", line 382, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "/usr/lib/python2.7/dist-packages/juju/agents/unit.py", line 226, in cb_watch_config_changed
    yield self.workflow.fire_transition("configure")
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1037, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python2.7/dist-packages/twisted/python/failure.py", line 382, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "/usr/lib/python2.7/dist-packages/juju/lib/statemachine.py", line 183, in fire_transition
    yield self.set_inflight(transition_id)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1037, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python2.7/dist-packages/twisted/python/failure.py", line 382, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "/usr/lib/python2.7/dist-packages/juju/lib/statemachine.py", line 292, in set_inflight
    yield self._store(state)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1037, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python2.7/dist-packages/twisted/python/failure.py", line 382, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "/usr/lib/python2.7/dist-packages/juju/unit/workflow.py", line 237, in _store
    yield retry_change(self._client, self.zk_state_path, update_state)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1037, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python2.7/dist-packages/twisted/python/failure.py", line 382, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "/usr/lib/python2.7/dist-packages/txzookeeper/utils.py", line 58, in retry_change
    new_content = yield change_function(content, stat)
  File "/usr/lib/python2.7/dist-packages/juju/unit/workflow.py", line 229, in update_state
    unit_data = yaml.load(content)
  File "/usr/lib/python2.7/dist-packages/yaml/__init__.py", line 69, in load
    loader = Loader(stream)
  File "/usr/lib/python2.7/dist-packages/yaml/loader.py", line 34, in __init__
    Reader.__init__(self, stream)
  File "/usr/lib/python2.7/dist-packages/yaml/reader.py", line 85, in __init__
    self.determine_encoding()
  File "/usr/lib/python2.7/dist-packages/yaml/reader.py", line 124, in determine_encoding
    self.update_raw()
  File "/usr/lib/python2.7/dist-packages/yaml/reader.py", line 178, in update_raw
    data = self.stream.read(size)
exceptions.AttributeError: 'NoneType' object has no attribute 'read'