Description of problem:
With yum 3.1.1 mock immediately stops with the following
error.
yum 3.1.0 causes no problem.

Version-Release number of selected component (if applicable):
yum-3.1.1-3.fc7
mock-0.6.11-1.fc7

How reproducible:
100%

Steps to Reproduce:
1. try "mock <some srpm>" with yum 3.1.1
2.
3.
  
Actual results:
DEBUG: Executing /usr/sbin/mock-helper yum --installroot
/var/lib/mock/fedora-development-i386-core/root install buildsys-build
Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
No Repositories Available to Set Up
Reading repository metadata in from local files
Parsing package install arguments
Traceback (most recent call last):
  File "/usr/libexec/mock-yum", line 12, in <module>
    yummain.main(sys.argv[1:])
  File "/usr/share/yum-cli/yummain.py", line 94, in main
    result, resultmsgs = base.doCommands()
  File "/usr/share/yum-cli/cli.py", line 263, in doCommands
    return self.yum_cli_commands[self.basecmd].doCommand(self, self.basecmd,
self.extcmds)
  File "/usr/share/yum-cli/yumcommands.py", line 134, in doCommand
    return base.installPkgs(extcmds)
  File "/usr/share/yum-cli/cli.py", line 436, in installPkgs
    self.pkgSack.matchPackageNames(arglist)
  File "/usr/lib/python2.5/site-packages/yum/packageSack.py", line 360, in
matchPackageNames
    unmatched = list(unmatched)
TypeError: 'NoneType' object is not iterable

Additional info:
F7T1 yum-3.1.0-2.fc7 has no problem.