virt-clone crashes whilst cloning a KVM vm

I'm unable to clone VMs using the standard virt-clone tool due to a crash in a python script. Here is the output that is generated in ~/.virtinst/virt-clone.log:

[Mon, 06 Aug 2012 11:45:01 virt-clone 14340] DEBUG (cli:220) Launched with command line:
/usr/bin/virt-clone --original-xml=/etc/libvirt/qemu/vm1.local.xml --name=vm2 --uuid=3f0f47af-6b61-4ed7-a295-736201c452f1 --mac=52:54:00:13:77:e0 --file=/home/robin/kvm/vm2/vm.qcow2
[Mon, 06 Aug 2012 11:45:01 virt-clone 14340] DEBUG (cli:326) Requesting libvirt URI default
[Mon, 06 Aug 2012 11:45:01 virt-clone 14340] DEBUG (cli:328) Received libvirt URI qemu:///system
[Mon, 06 Aug 2012 11:45:02 virt-clone 14340] DEBUG (CloneManager:399) Validating original guest parameters
[Mon, 06 Aug 2012 11:45:02 virt-clone 14340] DEBUG (CloneManager:408) Original XML:
<!--
WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
OVERWRITTEN AND LOST. Changes to this xml configuration should be made using:
  virsh edit vm1.local
or other application using the libvirt API.
-->

<domain type='kvm'>
  <name>vm1.local</name>
  <uuid>8fe324f0-b5cb-f6ad-a395-ca0104b9e96f</uuid>
  <memory>524288</memory>
  <currentMemory>524288</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc-1.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/home/robin/kvm/vm1/vm.qcow2'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0' unit='0'/>
    </disk>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='network'>
      <mac address='52:54:00:15:c9:05'/>
      <source network='default'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1'>
      <listen type='address' address='127.0.0.1'/>
    </graphics>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </memballoon>
  </devices>
</domain>

[Mon, 06 Aug 2012 11:45:03 virt-clone 14340] ERROR (cli:439) 'NoneType' object is not iterable
[Mon, 06 Aug 2012 11:45:03 virt-clone 14340] DEBUG (cli:440)
Traceback (most recent call last):
  File "/usr/bin/virt-clone", line 253, in <module>
    main()
  File "/usr/bin/virt-clone", line 232, in main
    design.setup_original()
  File "/usr/lib/python2.7/dist-packages/virtinst/CloneManager.py", line 411, in setup_original
    parsexml=self.original_xml)
  File "/usr/lib/python2.7/dist-packages/virtinst/Guest.py", line 233, in __init__
    caps=caps)
  File "/usr/lib/python2.7/dist-packages/virtinst/XMLBuilderDomain.py", line 398, in __init__
    self._parsexml(parsexml, parsexmlnode)
  File "/usr/lib/python2.7/dist-packages/virtinst/Guest.py", line 790, in _parsexml
    for node in self._xml_node.children:
TypeError: 'NoneType' object is not iterable

The command I'm using is:
/usr/bin/virt-clone --original-xml=/etc/libvirt/qemu/vm1.local.xml \
--name=vm2 \
--uuid=8a14d372-0d50-469f-87fc-c1efdb225638 \
--mac=52:54:00:21:a9:d4 \
--file=/home/robin/kvm/vm2/vm.qcow2

I have previously applied the following patch from bug #1008225, this applied without error and fixed the issue with ubuntu-vm-builder

https://bugs.launchpad.net/ubuntu/+source/vm-builder/+bug/1008225/+attachment/3208174/+files/lucid-vm.patch