package mailman3-web 0+20180916-1 failed to install/upgrade: installed mailman3-web package post-installation script subprocess returned error exit status 1

[tmoehle]

I was upgrading from Ubuntu 18.04 to 18.10 and mailman3-web returned an error while upgrading to the new version.

ProblemType: Package
DistroRelease: Ubuntu 18.10
Package: mailman3-web 0+20180916-1
ProcVersionSignature: Ubuntu 4.15.0-48.51-generic 4.15.18
Uname: Linux 4.15.0-48-generic x86_64
ApportVersion: 2.20.10-0ubuntu13.3
Architecture: amd64
Date: Sun May 12 13:58:49 2019
ErrorMessage: installed mailman3-web package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2015-11-02 (1286 days ago)
InstallationMedia: Ubuntu-Server 15.10 "Wily Werewolf" - Release amd64 (20151021)
PackageArchitecture: all
Python3Details: /usr/bin/python3.6, Python 3.6.8, python3-minimal, 3.6.7-1~18.10
PythonDetails: /usr/bin/python2.7, Python 2.7.16, python-minimal, 2.7.15-3
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu5
 apt 1.7.4
SourcePackage: mailman-suite
Title: package mailman3-web 0+20180916-1 failed to install/upgrade: installed mailman3-web package post-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to cosmic on 2019-05-12 (0 days ago)

[tmoehle (6-majl-9)]

Error persisted while upgrading from 18.10 to 19.04