package cron 3.0pl1-136ubuntu1 failed to install/upgrade: conffile difference visualizer subprocess returned error exit status 127

Failed during do-release-upgrade from 18.04.4 to 20.04.

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: cron 3.0pl1-136ubuntu1
ProcVersionSignature: Ubuntu 5.3.0-46.38~18.04.1-generic 5.3.18
Uname: Linux 5.3.0-46-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
Date: Fri Apr 24 13:03:47 2020
ErrorMessage: conffile difference visualizer subprocess returned error exit status 127
Python3Details: /usr/bin/python3.8, Python 3.8.2, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: /usr/bin/python2.7, Python 2.7.18rc1, python-is-python2, 2.7.17-4
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.2
SourcePackage: cron
Title: package cron 3.0pl1-136ubuntu1 failed to install/upgrade: conffile difference visualizer subprocess returned error exit status 127
UpgradeStatus: Upgraded to focal on 2020-04-24 (0 days ago)
modified.conffile..etc.crontab: [modified]
mtime.conffile..etc.crontab: 2019-12-19T12:01:39.171715