do-release-upgrade failed with message that ubuntu-minimal is missing

[Dmitry Lapshin]

That's pretty much it: i was trying to update 18.04 -> 20.04.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.38
ProcVersionSignature: Ubuntu 5.4.0-42.46~18.04.1-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.17
Architecture: amd64
CrashDB: ubuntu
Date: Wed Sep 2 18:13:39 2020
InstallationDate: Installed on 2016-04-23 (1592 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
ProcEnviron:
 TERM=tmux-256color
 PATH=(custom, no user)
 LANG=ru_RU.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-09-02 (0 days ago)
VarLogDistupgradeAptlog:
 Log time: 2020-09-02 18:12:21.116458
 Log time: 2020-09-02 18:12:49.832278
 Log time: 2020-09-02 18:13:38.361595
 Log time: 2020-09-02 18:13:54.216054