software-center crashed with TypeError in upstream_version_compare(): must be string, not None

[Rigved Rakshit]

Binary package hint: software-center

Description: Ubuntu Natty (development branch)
Release: 11.04
Installed: 3.1.24.3
Candidate: 3.1.24.3
Expected outcome: Software Center should have closed without any error.
Actual outcome: An error occurred while exiting the application. Something about a wrong return type from a function. It probably can be fixed by returning an empty string instead of "None".

Even though there is a bug report for this for Maverick, I still encountered this error in Narwhal.
In Maverick, the report number is #746120.

ProblemType: Crash
DistroRelease: Ubuntu 11.04
Package: software-center 3.1.24.3
ProcVersionSignature: Ubuntu 2.6.38-7.39-generic 2.6.38
Uname: Linux 2.6.38-7-generic i686
Architecture: i386
Date: Sun Apr 10 15:12:24 2011
ExecutablePath: /usr/share/software-center/software-center
InterpreterPath: /usr/bin/python2.7
LiveMediaBuild: Ubuntu 11.04 "Natty Narwhal" - Beta i386 (20110330)
ProcCmdline: /usr/bin/python /usr/bin/software-center
ProcEnviron:
 LANGUAGE=en_US:en
 LANG=en_US.UTF-8
 SHELL=/bin/bash
PythonArgs: ['/usr/bin/software-center']
SourcePackage: software-center
Title: software-center crashed with TypeError in upstream_version_compare(): must be string, not None
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare

[Apport retracing service (apport)]

Thank you for taking the time to report this crash and helping to make Ubuntu better. This particular crash has already been reported and is a duplicate of bug #746120, so 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.