dock_applet.py crashed with AttributeError in stop_drag_motion_timer(): 'NoneType' object has no attribute 'drag_ended'

[Sverrir Steindors]

I did not experience any abnormal behaviour and was not interacting with the dock when the error message came up. I'm using the Mutiny layout.

ProblemType: Crash
DistroRelease: Ubuntu 18.04
Package: mate-dock-applet 0.85-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-15.16-generic 4.15.15
Uname: Linux 4.15.0-15-generic x86_64
ApportVersion: 2.20.9-0ubuntu5
Architecture: amd64
CrashCounter: 1
CurrentDesktop: MATE
Date: Wed Apr 18 08:34:02 2018
ExecutablePath: /usr/lib/mate-applets/mate-dock-applet/dock_applet.py
InstallationDate: Installed on 2017-11-10 (158 days ago)
InstallationMedia: Ubuntu-MATE 17.10 "Artful Aardvark" - Release amd64 (20171018)
InterpreterPath: /usr/bin/python3.6
ProcCmdline: python3 /usr/lib/mate-applets/mate-dock-applet/dock_applet.py
Python3Details: /usr/bin/python3.6, Python 3.6.5, python3-minimal, 3.6.5-2
PythonArgs: ['/usr/lib/mate-applets/mate-dock-applet/dock_applet.py']
PythonDetails: /usr/bin/python2.7, Python 2.7.15rc1, python-minimal, 2.7.14-4
SourcePackage: mate-dock-applet
Title: dock_applet.py crashed with AttributeError in stop_drag_motion_timer(): 'NoneType' object has no attribute 'drag_ended'
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dialout dip lpadmin plugdev sambashare sudo