cvs2bzr crashed with IOError in setup(): [Errno 21] Is a directory: 'bzr/'

Was converting a cvs repository in order to move it from Sourceforge to Launchpad.

The repository which was being converted when the crash happened can get gotten from:

rsync -av rsync://pydns.cvs.sourceforge.net/cvsroot/pydns/* .

The exact command I used was:

cvs2bzr --username=kitterman --cvs-revnums --use-cvs --fallback-encoding=utf-8 -v --dumpfile bzr/ sf2/

ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: cvs2svn 2.3.0-2
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic-pae 3.2.14
Uname: Linux 3.2.0-24-generic-pae i686
ApportVersion: 2.0.1-0ubuntu7
Architecture: i386
Date: Sun Apr 29 01:01:42 2012
EcryptfsInUse: Yes
ExecutablePath: /usr/bin/cvs2bzr
InstallationMedia: Kubuntu 11.04 "Natty Narwhal" - Beta i386 (20110330)
InterpreterPath: /usr/bin/python2.7
PackageArchitecture: all
ProcCmdline: /usr/bin/python /usr/bin/cvs2bzr --username=kitterman --cvs-revnums --use-cvs --fallback-encoding=utf-8 -v --dumpfile bzr/ sf2/
ProcEnviron:
 SHELL=/bin/bash
 TERM=xterm
 LANG=en_US.UTF-8
 LANGUAGE=
PythonArgs: ['/usr/bin/cvs2bzr', '--username=kitterman', '--cvs-revnums', '--use-cvs', '--fallback-encoding=utf-8', '-v', '--dumpfile', 'bzr/', 'sf2/']
SourcePackage: cvs2svn
Title: cvs2bzr crashed with IOError in setup(): [Errno 21] Is a directory: 'bzr/'
UpgradeStatus: Upgraded to precise on 2012-04-09 (19 days ago)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare syslog wireshark