cannot upgrade to bionic beaver 18.04 lts

[Mridul Agarwal]

(appstreamcli:3249): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed

(appstreamcli:3249): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed

(appstreamcli:3249): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed

(appstreamcli:3249): 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 1:16.04.25
ProcVersionSignature: Ubuntu 4.13.0-39.44~16.04.1-generic 4.13.16
Uname: Linux 4.13.0-39-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.16
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sat Apr 28 15:55:06 2018
InstallationDate: Installed on 2018-03-10 (48 days ago)
InstallationMedia: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-04-28 (0 days ago)

[dino99 (9d9)]

Some ppas are used, so the packages version/naming cant be recognised to do the upgrade: downgrade them first , then try again to upgrade.

[Mona Brasseaux (mbrasseau)]

This is not a duplicate issue of bug #1611737 (ROS packages). It is not even presenting the same error message. It is a libappstream issue.

I was able to find the resolution here: https://askubuntu.com/questions/1051536/appstreamcli-appstream-system-cache-was-updated-but-problems-were-found-metad?noredirect=1&lq=1

First I attempted to reinstall with 'sudo apt install --reinstall libappstream2' because many are resolving the problem that way. My attempt returned an error that the program could not be found.

Then I used 'sudo apt-get purge libappstream2' and it both uninstalled whatever was there, then automatically installed the packages that were needed.

I was then able to proceed successfully with my upgrade to 18.04.1, from 16.04