software-center crashed with AttributeError in refresh_apps(): 'NoneType' object has no attribute 'clear_model'

[Bob Bib]

1) double-clicked on a DEB file, so Ubuntu Software Center window (with "waiting/refreshing" animation at the center) opened;
2) Help -> About, Close;
3) View -> Canonical-Maintained Software;
4) still "waiting/refreshing", so I closed the window... oops, it crashed!

ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: software-center 5.1.11
ProcVersionSignature: Ubuntu 3.2.0-18.28-generic 3.2.9
Uname: Linux 3.2.0-18-generic x86_64
ApportVersion: 1.94.1-0ubuntu1
Architecture: amd64
Date: Sat Mar 10 01:40:47 2012
ExecutablePath: /usr/share/software-center/software-center
InterpreterPath: /usr/bin/python2.7
PackageArchitecture: all
ProcCmdline: /usr/bin/python /usr/bin/software-center /home/username/apps/aircrack-ng/aircrack-ng/aircrack-ng_1.1~svn2127-1_amd64.deb
PythonArgs: ['/usr/bin/software-center', '/home/username/apps/aircrack-ng/aircrack-ng/aircrack-ng_1.1~svn2127-1_amd64.deb']
SourcePackage: software-center
Title: software-center crashed with AttributeError in refresh_apps(): 'NoneType' object has no attribute 'clear_model'
UpgradeStatus: Upgraded to precise on 2012-03-07 (2 days ago)
UserGroups: adm admin audio cdrom dialout dip fax floppy fuse kismet kvm lpadmin netdev plugdev powerdev sambashare scanner tape vboxusers video wireshark

[Launchpad Janitor (janitor)]

This bug was fixed in the package software-center - 5.1.13

---------------
software-center (5.1.13) precise; urgency=low

  [ Anthony Lenton ]
  * lp:~elachuni/software-center/pep8-test-part5,
    lp:~elachuni/software-center/pep8-test-part6,
    lp:~elachuni/software-center/pep8-test-part7,
    lp:~elachuni/software-center/pep8-test-part8,
    lp:~elachuni/software-center/pep8-test-part9,
    lp:~elachuni/software-center/pep8-test-part10,
    lp:~elachuni/software-center/pep8-test-part11,
    lp:~elachuni/software-center/pep8-test-part12,
    lp:~elachuni/software-center/pep8-test-part13,
    lp:~elachuni/software-center/pep8-test-part14,
    lp:~elachuni/software-center/pep8-test-part15,
    lp:~elachuni/software-center/pep8-test-part16,
    lp:~elachuni/software-center/pep8-test-part17,
    lp:~elachuni/software-center/pep8-test-part18,
    lp:~elachuni/software-center/pep8-test-part19,
    lp:~elachuni/software-center/pep8-test-part20,
    lp:~elachuni/software-center/pep8-test-part21,
    lp:~elachuni/software-center/pep8-test-part22:
    - many, many, many pep8 fixes
  * lp:~elachuni/software-center/unify-ussoc-envvar:
    - fix USSOC_SERVICE_URL env variable

  [ Gabor Kelemen ]
  * lp:~kelemeng/software-center/bug953812: (LP: #953812)
    - Translate review sorting criteria
    - Fix the Recommendation spinner text translations

  [ Michael Vogt ]
  * lp:~mvo/software-center/small-sso-fixes:
    - fix the clear_credentials() call if a token is no
      longer valid
  * lp:~mvo/software-center/lp955005:
    - don't display ratings for the case where an app
      cannot be found (LP: #955005)
  * lp:~mvo/software-center/opengl-driver-blacklist:
    - add support for video driver blacklisting
  * lp:~mvo/software-center/lp856559:
    - fix case where the search term is not always
      cleared in the search entry (LP: #856559)
  * lp:~mvo/software-center/misc-fixes:
    - when a package can not be authenticated, do not fail
      (hard) but instead offer to "repair" the situation using
      a "reload" and try the install again (LP: #876278)
    - do not crash in if os.makedirs has a race condition
      (LP: #956680)
    - fix the proxy handling with 12.04 as the "enabled" property
      is deprecated now. it will also not mess with the proxy
      environment on non-gnome systems (LP: #742564)
  * lp:~mvo/software-center/lp780812:
    - ensure that the distroseries is updated in the sources
      deb line when updating a purchased item (LP: #780812)
  * lp:~mvo/software-center/recommendations-opt-out:
    - fix double-results when opting-in and back out of of
      the recommendations service repeatedly
  * lp:~mvo/software-center/tos-dialog:
    - display a terms-of-service dialog before the first purchase
  * lp:~mvo/software-center/lp957599:
    - add a new unit test test_spawn_helper.py
  * lp:~mvo/software-center/track-db-open:
    - improve db logging

  [ Gary Lasker ]
  * lp:~gary-lasker/software-center/fix-lp955048:
    - String fix for the "Recommended For You" panel. LP: #955048
  * lp:~gary-lasker/software-center/fix-lp856559:
    - Clears the search entry field before doing a reinstall
      previous purchases (LP: #85655...