unity-mail crashed with AttributeError in __init__(): module 'platform' has no attribute 'linux_distribution'

[Norbert]

Does not start on Focal:

$ apt-cache policy unity-mail
unity-mail:
  Installed: 1.7.5.1
  Candidate: 1.7.5.1
  Version table:
 *** 1.7.5.1 500
        500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
        500 http://archive.ubuntu.com/ubuntu focal/universe i386 Packages
        100 /var/lib/dpkg/status

$ unity-mail
Traceback (most recent call last):
  File "/usr/bin/unity-mail", line 12, in <module>
    UnityMail()
  File "/usr/share/unity-mail/UnityMail/application.py", line 165, in __init__
    self.oMessagingMenu = MessagingMenu(self.onMenuItemClicked, self.openDialog, self.updateMessageAges)
  File "/usr/share/unity-mail/UnityMail/__init__.py", line 121, in __init__
    nVersion = int(platform.linux_distribution()[1].replace('.', ''))
AttributeError: module 'platform' has no attribute 'linux_distribution'

ProblemType: Crash
DistroRelease: Ubuntu 20.04
Package: unity-mail 1.7.5.1
ProcVersionSignature: Ubuntu 5.4.0-80.90-generic 5.4.124
Uname: Linux 5.4.0-80-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CrashCounter: 1
CurrentDesktop: MATE
Date: Wed Aug 11 16:45:07 2021
ExecutablePath: /usr/share/unity-mail/unity-mail
ExecutableTimestamp: 1495529470
InstallationDate: Installed on 2020-04-23 (474 days ago)
InstallationMedia: Ubuntu-MATE 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
InterpreterPath: /usr/bin/python3.8
PackageArchitecture: all
ProcCmdline: /usr/bin/python3 /usr/bin/unity-mail
ProcCwd: /home/mate
Python3Details: /usr/bin/python3.8, Python 3.8.10, python3-minimal, 3.8.2-0ubuntu2
PythonArgs: ['/usr/bin/unity-mail']
PythonDetails: /usr/bin/python3.8, Python 3.8.10, python-is-python3, 3.8.2-4
SourcePackage: unity-mail
Title: unity-mail crashed with AttributeError in __init__(): module 'platform' has no attribute 'linux_distribution'
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin lxd plugdev sambashare sudo