upgrade from 16.04 to 18.04 not possible

[Rudolf Metzler]

appstreamcli:3751): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed

(appstreamcli:3751): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed

(appstreamcli:3751): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed

(appstreamcli:3751): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed

(appstreamcli:3751): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed

(appstreamcli:3751): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed
AppStream cache update completed, but some metadata was ignored due to errors.

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done

Calculating the changes

Calculating the changes

Could not calculate the upgrade

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.25
ProcVersionSignature: Ubuntu 4.15.0-29.31~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Tue Jul 24 19:09:00 2018
InstallationDate: Installed on 2018-06-18 (35 days ago)
InstallationMedia: Ubuntu 16.04.4 LTS "Xenial Xerus" - Release amd64 (20180228)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-07-24 (0 days ago)

[Karun (karun-gahlawat)]

i am facing this issue as well. can't understand why though. i have disabled all non ubuntu packages from apt source to the best of my knowledge. any help is appreciated

karun@karunlindev3:~$ sudo do-release-upgrade
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [819 B]
Get:2 Upgrade tool [1,258 kB]
Fetched 1,259 kB in 0s (0 B/s)
authenticate 'bionic.tar.gz' against 'bionic.tar.gz.gpg'
extracting 'bionic.tar.gz'

Reading cache

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done
Hit http://us.archive.ubuntu.com/ubuntu xenial InRelease
Hit http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease
Hit http://us.archive.ubuntu.com/ubuntu xenial-backports InRelease
Get:1 http://security.ubuntu.com/ubuntu xenial-security InRelease [107 kB]
Fetched 107 kB in 0s (0 B/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done

Updating repository information
Get:1 http://us.archive.ubuntu.com/ubuntu bionic InRelease [242 kB]
Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [83.2 kB]
Get:3 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
Get:4 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]
Get:5 http://us.archive.ubuntu.com/ubuntu bionic/main amd64 Packages [1,019 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu bionic/main i386 Packages [1,007 kB]
Get:7 http://us.archive.ubuntu.com/ubuntu bionic/main Translation-en [516 kB]
Get:8 http://us.archive.ubuntu.com/ubuntu bionic/main amd64 DEP-11 Metadata [477 kB]
Get:9 http://us.archive.ubuntu.com/ubuntu bionic/main DEP-11 ...

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.