TypeError: 'NoneType' object is not callable

[Whitney Guevara]

/usr/bin/update-manager:28: PyGIWarning: Gtk was imported without specifying a version first. Use gi.require_version('Gtk', '3.0') before import to ensure that the right version gets loaded.
  from gi.repository import Gtk
/usr/lib/python3/dist-packages/UpdateManager/UnitySupport.py:29: PyGIWarning: Dbusmenu was imported without specifying a version first. Use gi.require_version('Dbusmenu', '0.4') before import to ensure that the right version gets loaded.
  from gi.repository import Dbusmenu, Unity
/usr/lib/python3/dist-packages/UpdateManager/UnitySupport.py:29: PyGIWarning: Unity was imported without specifying a version first. Use gi.require_version('Unity', '7.0') before import to ensure that the right version gets loaded.
  from gi.repository import Dbusmenu, Unity

(update-manager:26973): GLib-CRITICAL **: g_hash_table_destroy: assertion 'hash_table != NULL' failed

(update-manager:26973): GLib-CRITICAL **: g_hash_table_destroy: assertion 'hash_table != NULL' failed
Exception ignored in: <object repr() failed>
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/gi/overrides/GLib.py", line 253, in __del__
TypeError: 'NoneType' object is not callable

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.21
ProcVersionSignature: Ubuntu 4.8.0-46.49~16.04.1-generic 4.8.17
Uname: Linux 4.8.0-46-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Fri May 12 15:42:43 2017
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-04-03 (39 days ago)
InstallationMedia: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: No upgrade log present (probably fresh install)
VarLogDistupgradeTermlog:

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Janek37 (j-sz)]

I get this bug on Ubuntu Mate 16.04 when another process is updating some packages.

[Aarsh S Talati (aarshstalati1989-l)]

Installing update notifier fixed the problem for me in Ubuntu-MATE 18.04 LTS. Code: `$ sudo apt-get install update-notifier`