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

Mey mpt! Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported and is a duplicate of bug 920196, so it is being marked as such. Please look at the other bug report to see if there is any missing information that you can provide, or to see if there is a workaround for the bug. Additionally, any further discussion regarding the bug should occur in the other report. Please continue to report any other bugs you may find.

Thanks again!

On further investigation, this does not appear to be a duplicate of bug 920196, but rather a different manifestation of a class of bug where the apt cache is being accessed before it is ready.

I'll keep this open for tracing as we tackle the various failure cases for this bug.

Thanks!

Branch contains a proposed fix for this palindromatic-numbered bug report.

Hello Matthew, or anyone else affected,

Accepted software-center into precise-proposed. The package will build now and be available in a few hours. Please test and give feedback here. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you in advance!

This bug was fixed in the package software-center - 5.2.2

---------------
software-center (5.2.2) precise-proposed; urgency=low

  [ Michael Vogt ]
  * lp:~mvo/software-center/whatsnew-leak-lp985389:
    - search filter fix for the case when the "installed-only"
      filter leaks into subsequent searches (LP: #985389)
  * lp:~mvo/software-center/fix-lp994632:
    - add a dep to ensure we get the correct ubuntu-sso-client-gtk
      (LP: #994632)
  * lp:~mvo/software-center/proper-error-on-unknown-files:
    - show a proper error message when attempting to open unknown
      file types (LP: #944868)
  * lp:~mvo/software-center/lp921799:
    - fix crash when decoding screenshots JSON (LP: #921799)
  * lp:~mvo/software-center/lp959612:
    - fix crash when selecting the Installed view very quickly
      after startup (LP: #959612)

  [ Ken VanDine ]
  * lp:~ken-vandine/software-center/lp_982567:
    - Check if the proxy is enabled, if the proxy host is set but not
      enabled we shouldn't attempt to use the proxy (LP: #982567)

  [ Gary Lasker ]
  * lp:~gary-lasker/software-center/fix-crash-lp969732:
    - need to explicitly declare the needs-refresh signal in the
      AppTreeStore class to prevent a crash (LP: #969732)
  * lp:~gary-lasker/software-center/fix-crash-lp870822:
    - don't crash if we don't get a pkgversion object back
      (LP: #870822)
  * lp:~gary-lasker/software-center/fix-shutdown-crash-lp996333:
    - never crash when writing out the software center config file on
      shutdown (LP: #996333)
  * lp:~gary-lasker/software-center/fix-makedirs-race-crashes:
    - fix crash on race when creating the cache or config directories
      (LP: #743003, LP: #621182)
  * lp:~gary-lasker/software-center/fix-crash_lp973379:
    - ensure that the cache is ready before using the recommender
      service (LP: #973379 )
  * lp:~gary-lasker/software-center/toolbar-buttons-insensitive-during-startup:
    - set the toolbar buttons insensitive for the duration of time that the
      lobby panels are initializing (LP: #999486, LP: #994341)

  [ Robert Roth ]
  * lp:~evfool/software-center/bug532072:
    - escape markup for support info and license (LP: #993279)
    - ellipsize summary at trailing end (LP: #532072)
  * lp:~evfool/software-center/lp626037:
    - subtle background color tweak for consistency
      between views (LP: #626037)
  * lp:~evfool/software-center/lp835005:
    - no need for the software-properties dialog to be modal
      to software-center (LP: #835005)
  * lp:~evfool/software-center/lp839389:
    - don't display an "icon not found" image in the Unity
      launcher when a report a review window is opened (LP: #839389)
  * lp:~evfool/software-center/867588:
    - capitalize the first letter of the package summary
      (LP: #867588)
  * lp:~evfool/software-center/lp876657:
    - make sure the search field does not disappear when an
      install or remove is in progress (LP: #876657)
  * lp:~evfool/software-center/lp987797:
    - fix alignment in the reviews part of the appdetails (LP: #987797)
  * lp:~evfool/software-center/lp844768:
    - show a indeterminate progress bar when software-center waits for
      another ...