<type 'exceptions.TypeError'>: 'NoneType' object is not iterable

/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/Twisted-8.2.0-py2.5-macosx-10.3-i386.egg/twisted/internet/defer.py, line 328 in _runCallbacks
326
                    self._runningCallbacks = True
327
                    try:
328
                        self.result = callback(self.result, *args, **kw)
329
                    finally:
Locals
callback<function <lambda> at 0x3743b30>
self<Deferred at 0x328f878 current result: <twisted.python.failure.Failure <type 'exceptions.TypeError'>>>
args()
kw{}
/Users/wonwinmcbrootles/playground/allmydata/tahoe/trunk/trunk/src/allmydata/mutable/filenode.py, line 238 in <lambda>
236
        # MFN instance.
237
        d = defer.Deferred()
238
        self._serializer.addCallback(lambda ignore: cb(*args, **kwargs))
239
        # we need to put off d.callback until this Deferred is finished being
Locals
ignoreNone
cb<bound method MutableFileNode._try_once_to_download_version of <MutableFileNode 328f648 RW wzpoc5l4>>
args(<allmydata.mutable.servermap.ServerMap instance at 0x33a9a58>, None, True)
kwargs{}
Globals
defer<module 'twisted.internet.defer' from '/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/Twisted-8.2.0-py2.5-macosx-10.3-i386.egg/twisted/internet/defer.pyc'>
/Users/wonwinmcbrootles/playground/allmydata/tahoe/trunk/trunk/src/allmydata/mutable/filenode.py, line 428 in _try_once_to_download_version
426
    def _try_once_to_download_version(self, servermap, version,
427
                                      fetch_privkey=False):
428
        r = Retrieve(self, servermap, version, fetch_privkey)
429
        history = self._client.get_history()
Locals
servermap<allmydata.mutable.servermap.ServerMap instance at 0x33a9a58>
self<MutableFileNode 328f648 RW wzpoc5l4>
versionNone
fetch_privkeyTrue
Globals
Retrieve<class allmydata.mutable.retrieve.Retrieve at 0x31aea50>
/Users/wonwinmcbrootles/playground/allmydata/tahoe/trunk/trunk/src/allmydata/mutable/retrieve.py, line 113 in __init__
111
        self._status.set_active(True)
112
        (seqnum, root_hash, IV, segsize, datalength, k, N, prefix,
113
         offsets_tuple) = self.verinfo
114
        self._status.set_size(datalength)
Locals
verinfoNone
prefix'6s64w'
self<allmydata.mutable.retrieve.Retrieve instance at 0x37a4828>

<type 'exceptions.TypeError'>: 'NoneType' object is not iterable