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

[APolihron]

after i open 2 folders in caja and i try to swich form folder 1 to folder 2

ProblemType: Crash
DistroRelease: Ubuntu 16.04
Package: mate-dock-applet 0.67-3
ProcVersionSignature: Ubuntu 4.4.0-7.22-generic 4.4.2
Uname: Linux 4.4.0-7-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CurrentDesktop: MATE
Date: Fri Feb 26 17:33:52 2016
ExecutablePath: /usr/lib/mate-applets/mate-dock-applet/dock_applet.py
InstallationDate: Installed on 2016-02-26 (0 days ago)
InstallationMedia: Ubuntu-MATE 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160224)
InterpreterPath: /usr/bin/python3.5
ProcCmdline: python3 /usr/lib/mate-applets/mate-dock-applet/dock_applet.py
PythonArgs: ['/usr/lib/mate-applets/mate-dock-applet/dock_applet.py']
SourcePackage: mate-dock-applet
Title: dock_applet.py crashed with AttributeError in minimize_or_restore_windows(): 'NoneType' object has no attribute 'activate'
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo

[Artur Rona (ari-tczew)]

This bug was fixed in the package mate-dock-applet - 0.69-1
Sponsored for Martin Wimpress (flexiondotorg)

---------------
mate-dock-applet (0.69-1) unstable; urgency=medium

  [ Martin Wimpress ]
  * New upstream release. (LP:#1555324, LP:#1550392, LP:#1554128).

  [ Mike Gabriel ]
  * debian/control:
    + Bump Standards: to 3.9.7. No changes needed.

 -- Mike Gabriel <email address hidden> Mon, 14 Mar 2016 15:17:04 +0100