TypeError: int() argument must be a string or a number, not 'NoneType'

$ cat build.sh
# --firstboot firstboot.sh
# --firstlogin firstboot.sh

vmbuilder xen ubuntu \
    --suite lucid --flavour virtual --arch amd64 \
    --part partitions.txt \
    --user ubuntu --name Ubuntu \
    --components main,universe \
    --addpkg openssh-server

$ sudo ./build.sh
2010-03-30 06:21:34,784 INFO : Calling hook: preflight_check
2010-03-30 06:21:34,790 INFO : Calling hook: set_defaults
2010-03-30 06:21:34,791 INFO : Calling hook: bootstrap
2010-03-30 06:23:18,089 INFO : Calling hook: configure_os
2010-03-30 06:23:28,132 INFO : update-alternatives: error: no alternatives for rsh.
2010-03-30 06:23:28,362 INFO : update-alternatives: error: no alternatives for rlogin.
2010-03-30 06:23:28,585 INFO : update-alternatives: error: no alternatives for rcp.
2010-03-30 06:23:30,962 INFO : Creating SSH2 RSA key; this may take some time ...
2010-03-30 06:23:31,340 INFO : Creating SSH2 DSA key; this may take some time ...
2010-03-30 06:23:31,865 INFO :
2010-03-30 06:23:31,867 INFO : Warning: Fake initctl called, doing nothing
2010-03-30 06:23:31,880 INFO :
2010-03-30 06:23:31,880 INFO : Warning: Fake initctl called, doing nothing
2010-03-30 06:23:34,860 INFO : Calling hook: post_install
Traceback (most recent call last):
  File "/usr/bin/vmbuilder", line 24, in <module>
    cli.main()
  File "/usr/lib/python2.6/dist-packages/VMBuilder/contrib/cli.py", line 105, in main
    self.set_disk_layout(hypervisor)
  File "/usr/lib/python2.6/dist-packages/VMBuilder/contrib/cli.py", line 203, in set_disk_layout
    hypervisor.add_filesystem(elements[1], default_filesystem, mntpnt='/')
  File "/usr/lib/python2.6/dist-packages/VMBuilder/hypervisor.py", line 51, in add_filesystem
    fs = Filesystem(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/VMBuilder/disk.py", line 324, in __init__
    self.set_type(type)
  File "/usr/lib/python2.6/dist-packages/VMBuilder/disk.py", line 415, in set_type
    if int(type) == type:
TypeError: int() argument must be a string or a number, not 'NoneType'

$ dpkg -l python-vm-builder
python-vm-builder 0.12.2-0ubuntu4