Gnome crashes with using keystroke to lock screen while viewing window previews in dock.

Steps to reproduce:

1. View the window previews from the dock (right click on the icon -> All Windows).
2. While viewing these previews, click the keyboard shortcut to lock the screen (Sup + L).
3. Gnome crashes.

12:01:35 in ~
➜ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic

12:01:38 in ~
➜ uname -a
Linux globemasteriii 4.15.0-34-generic #37-Ubuntu SMP Mon Aug 27 15:21:48 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

➜ cat gnome-version.xml
<?xml version="1.0" encoding="UTF-8"?>
<gnome-version>
 <platform>3</platform>
 <minor>28</minor>
 <micro>2</micro>
 <distributor>Ubuntu</distributor>

</gnome-version>%