dock_applet.py crashed with NameError in applet_drag_motion(): name 'app' is not defined

[BertN45]

Moved terminal to dock and started the terminal from the dock, which seemed to cause the crash.

ProblemType: Crash
DistroRelease: Ubuntu 18.04
Package: mate-dock-applet 0.81-0ubuntu1
ProcVersionSignature: Ubuntu 4.13.0-32.35-generic 4.13.13
Uname: Linux 4.13.0-32-generic x86_64
ApportVersion: 2.20.8-0ubuntu10
Architecture: amd64
CurrentDesktop: MATE
Date: Tue Feb 20 20:00:57 2018
ExecutablePath: /usr/lib/mate-applets/mate-dock-applet/dock_applet.py
InstallationDate: Installed on 2018-02-20 (0 days ago)
InstallationMedia: Ubuntu-MATE 18.04 LTS "Bionic Beaver" - Alpha amd64 (20180220)
InterpreterPath: /usr/bin/python3.6
ProcCmdline: python3 /usr/lib/mate-applets/mate-dock-applet/dock_applet.py
Python3Details: /usr/bin/python3.6, Python 3.6.4+, python3-minimal, 3.6.4-1
PythonArgs: ['/usr/lib/mate-applets/mate-dock-applet/dock_applet.py']
PythonDetails: /usr/bin/python2.7, Python 2.7.14+, python-minimal, 2.7.14-4
SourcePackage: mate-dock-applet
Title: dock_applet.py crashed with NameError in applet_drag_motion(): name 'app' is not defined
Traceback:
 Traceback (most recent call last):
   File "/usr/lib/mate-applets/mate-dock-applet/dock_applet.py", line 513, in applet_drag_motion
     if app is None:
 NameError: name 'app' is not defined
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo vboxsf

[Launchpad Janitor (janitor)]

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

[rhhoek (r-h-hoek)]

First selected compiz in MATE Tweak -> Windows -> Window manger
Then selected 'Dock Preferences' of the Munity Dock.
then Windows -> Windows selection -> 'From window thumbnail prefiews (requires Compiz)'
crash

[Andamo Deming (andamod)]

I had the same problem when moving Terminator from the desktop to the dock.

[Launchpad Janitor (janitor)]

[Expired for mate-dock-applet (Ubuntu) because there has been no activity for 60 days.]