Description of problem: Once yum-plugin-rpm-warm-cache is installed on F-11 every yum transaction (install/update/remove) will output this errors few second after it has suceed. 
This seems to be related to some post-transaction plugin, and maybe refresh-packagekit...

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Traceback (most recent call last):
  File "/usr/share/PackageKit/helpers/yum/yumBackend.py", line 2461, in _check_init
    self.yumbase.repos.doSetup()
  File "/usr/lib/python2.6/site-packages/yum/repos.py", line 79, in doSetup
    self.ayum.plugins.run('postreposetup')
  File "/usr/lib/python2.6/site-packages/yum/plugins.py", line 179, in run
    func(conduitcls(self, self.base, conf, **kwargs))
  File "/usr/lib/yum-plugins/rpm-warm-cache.py", line 32, in postreposetup_hook
    cmd = commands[0]
TypeError: 'NoneType' object is unsubscriptable
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Version-Release number of selected component (if applicable):
yum-utils-1.1.21-2.fc11.noarch

How reproducible:
always

Steps to Reproduce:
1. yum install yum-plugins\*
2. yum install any_random_package
3. once package is installed, an error message is seen about the rpm-warm-cache yum plugin.
  
Actual results:
A system error is seen

Expected results:
should process quitely

Additional info: