[Bug 1811597] Re: update from 16.04 to 18.04 failed

[Ubuntu Foundations Team Bug Bot]

*** This bug is a duplicate of bug 1611737 ***
    https://bugs.launchpad.net/bugs/1611737

** Tags added: xenial2bionic

** This bug has been marked a duplicate of bug 1611737
   Can't upgrade from a release if ros packages are  installed from ROS servers

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https://bugs.launchpad.net/bugs/1811597

Title:
  update from 16.04 to 18.04  failed

Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  /usr/lib/python3/dist-packages/DistUpgrade/ReleaseNotesViewerWebkit.py:33: PyGIWarning: WebKit2 was imported without specifying a version first. Use gi.require_version('WebKit2', '4.0') before import to ensure that the right version gets loaded.
    from gi.repository import WebKit2 as WebKit
  Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
  autenticar «bionic.tar.gz» contra «bionic.tar.gz.gpg» 
  extrayendo «bionic.tar.gz»

  (appstreamcli:19254): GLib-CRITICAL **: g_strchug: assertion 'string
  != NULL' failed

  (appstreamcli:19254): GLib-CRITICAL **: g_strchomp: assertion 'string
  != NULL' failed

  (appstreamcli:19254): GLib-CRITICAL **: g_strchug: assertion 'string
  != NULL' failed

  (appstreamcli:19254): GLib-CRITICAL **: g_strchomp: assertion 'string
  != NULL' failed

  (appstreamcli:19254): GLib-CRITICAL **: g_strchug: assertion 'string
  != NULL' failed

  (appstreamcli:19254): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed
  AppStream cache update completed, but some metadata was ignored due to errors.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.26
  Uname: Linux 4.12.14-041214-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.18
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: Unity
  Date: Sun Jan 13 19:00:48 2019
  InstallationDate: Installed on 2016-05-09 (979 days ago)
  InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2019-01-13 (0 days ago)
  VarLogDistupgradeTermlog:

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