Error trying to empty a USB stick: 'NoneType' object has no attribute 'get_cached_property'

I'm getting the following error message when trying to empty an USB stick, after entering the password:

---
org.freedesktop.DBus.Python.AttributeError: Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/dbus/service.py", line 707, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/usr/share/usb-creator/usb-creator-helper", line 218, in Format
    parent_dev = _get_parent_object(udisks, device)
  File "/usr/share/usb-creator/usb-creator-helper", line 49, in _get_parent_object
    parent = partition.get_cached_property('Table').get_string()
AttributeError: 'NoneType' object has no attribute 'get_cached_property'
---

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: usb-creator-gtk 0.2.56
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu2
Architecture: amd64
CurrentDesktop: Unity
Date: Mon Apr 14 20:15:49 2014
EcryptfsInUse: Yes
InstallationDate: Installed on 2012-03-16 (758 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120316)
SourcePackage: usb-creator
UpgradeStatus: Upgraded to trusty on 2013-10-23 (173 days ago)