update-manager crashed with TypeError in update(): argument of type 'NoneType' is not iterable

Trying to upgrade with a poor quality connection.

ProblemType: Crash
DistroRelease: Ubuntu 20.04
Package: update-manager 1:20.04.4
ProcVersionSignature: Ubuntu 5.4.0-21.25-generic 5.4.27
Uname: Linux 5.4.0-21-generic x86_64
ApportVersion: 2.20.11-0ubuntu25
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Apr 8 14:52:29 2020
ExecutablePath: /usr/bin/update-manager
ExecutableTimestamp: 1586265970
InstallationDate: Installed on 2019-02-21 (412 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
InterpreterPath: /usr/bin/python3.8
PackageArchitecture: all
ProcCmdline: /usr/bin/python3 /usr/bin/update-manager --no-update --no-focus-on-map
ProcCwd: /home/nicolas
ProcEnviron:
 PATH=(custom, user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
Python3Details: /usr/bin/python3.8, Python 3.8.2, python3-minimal, 3.8.2-0ubuntu2
PythonArgs: ['/usr/bin/update-manager', '--no-update', '--no-focus-on-map']
PythonDetails: /usr/bin/python3.8, Python 3.8.2, unpackaged
SourcePackage: update-manager
Title: update-manager crashed with TypeError in update(): argument of type 'NoneType' is not iterable
UpgradeStatus: Upgraded to focal on 2020-03-20 (19 days ago)
UserGroups: adm cdrom dialout dip docker lpadmin plugdev sambashare sudo