Description of problem:
The following was filed automatically by anaconda:
anaconda 18.37.11 exception report
Traceback (most recent call first):
  File "/usr/lib/python2.7/site-packages/pyanaconda/storage/__init__.py", line 1189, in destroyDevice
    if device.format.exists and device.format.type:
  File "/usr/lib/python2.7/site-packages/pyanaconda/storage/__init__.py", line 859, in removeEmptyExtendedPartitions
    self.destroyDevice(extended)
  File "/usr/lib/python2.7/site-packages/pyanaconda/storage/__init__.py", line 799, in clearPartitions
    self.removeEmptyExtendedPartitions()
  File "/usr/lib/python2.7/site-packages/pyanaconda/kickstart.py", line 445, in execute
    storage.clearPartitions()
  File "/usr/lib/python2.7/site-packages/pyanaconda/kickstart.py", line 1480, in doKickstartStorage
    ksdata.clearpart.execute(storage, ksdata, instClass)
  File "/usr/lib/python2.7/site-packages/pyanaconda/ui/gui/spokes/storage.py", line 399, in _doExecute
    doKickstartStorage(self.storage, self.data, self.instclass)
  File "/usr/lib/python2.7/threading.py", line 504, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib/python2.7/site-packages/pyanaconda/threads.py", line 91, in run
    threading.Thread.run(self, *args, **kwargs)
AttributeError: 'NoneType' object has no attribute 'format'

Additional info:
cmdline:        /usr/bin/python  /sbin/anaconda --liveinst --method=livecd:///dev/mapper/live-osimg-min --lang en_US.UTF-8
cmdline_file:   initrd=/ubninit root=live:UUID=4C6A-D724 rootfstype=auto ro rd.live.image quiet  rhgb rd.luks=0 rd.md=0 rd.dm=0 BOOT_IMAGE=/ubnkern 
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         3.6.10-4.fc18.i686
other involved packages: python-libs-2.7.3-13.fc18.i686
package:        anaconda-18.37.11-1.fc18.i686
packaging.log:  
product:        Fedora
release:        Fedora release 18 (Spherical Cow)
type:           libreport
version:        18