[Bug 1825886] Re: Unattended-upgrades may crash when a package does not have a candidate

[Balint Reczey]

Verified on Disco, Cosmic, Bionic and Xenial, the error is not seen on
any of the releases:

https://errors.ubuntu.com/?release=Ubuntu%2019.04&package=unattended-
upgrades&period=week&version=1.10ubuntu5.1

https://errors.ubuntu.com/?release=Ubuntu%2018.10&package=unattended-
upgrades&period=week&version=1.5ubuntu3.18.10.4

https://errors.ubuntu.com/?release=Ubuntu%2018.04&package=unattended-
upgrades&period=week&version=1.1ubuntu1.18.04.11

https://errors.ubuntu.com/?release=Ubuntu%2016.04&package=unattended-
upgrades&period=week&version=1.1ubuntu1.18.04.7~16.04.3

** Tags removed: verification-needed verification-needed-bionic verification-needed-cosmic verification-needed-disco verification-needed-xenial
** Tags added: verification-done verification-done-bionic verification-done-cosmic verification-done-disco verification-done-xenial

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https://bugs.launchpad.net/bugs/1825886

Title:
  Unattended-upgrades may crash when a package does not have a candidate

Status in unattended-upgrades package in Ubuntu:
  Fix Released
Status in unattended-upgrades source package in Xenial:
  Fix Committed
Status in unattended-upgrades source package in Bionic:
  Fix Committed
Status in unattended-upgrades source package in Cosmic:
  Fix Committed
Status in unattended-upgrades source package in Disco:
  Fix Committed

Bug description:
  [Impact]

   * Unattended-upgrades may crash when a package in apt's cache does not have a candidate and it is visited when finding packages to adjust.
   * The crash occurs when apt.Package.candidate is None and the fix is checking if .candidate is truthy and it that case is safe to reference the .dependencies attribute.

  [Test Case]

   * Watch the error not happening anymore.

  [Regression Potential]

   * The fix is very small and is not likely to cause any regression.

  [Original Bug Text]

  The Ubuntu Error Tracker has been receiving reports about a problem regarding unattended-upgrades.  This problem was most recently seen with package version 1.10ubuntu5, the problem page at https://errors.ubuntu.com/problem/0d08f995622277f81d276f1eae7e1a722e3627de contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
  If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at http://forms.canonical.com/reports/.

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