Update to 20.04 crashes with non-informative error. KDE Neon distro.

[Andrew]

The distro is KDE Neon, but the error message instructed to send the bug with `ubuntu-bug ubuntu-release-upgrader-core`.

ProblemType: Bug
DistroRelease: KDE neon 18.04
Package: ubuntu-release-upgrader-core 1:18.04.38+p18.04+git20200803.1136 [origin: unknown]
ProcVersionSignature: Ubuntu 5.4.0-42.46~18.04.1-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.16
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Thu Aug 20 07:34:56 2020
InstallationDate: Installed on 2020-06-12 (68 days ago)
InstallationMedia: neon user "Bionic" - Build amd64 LIVE Binary 20200609-12:34
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-08-20 (0 days ago)
VarLogDistupgradeTermlog: