Unclear exception when using hotkey + grid on IntelliJ window

[colindean]

./window_mgmt.lua:53: attempt to index a nil value stack traceback: ./window_mgmt.lua:53: in function <./window_mgmt.lua:53> [C]: in function 'xpcall' /usr/local/share/lua/5.2/mjolnir/hotkey.lua:23: in function </usr/local/share/lua/5.2/mjolnir/hotkey.lua:21>

window_mgmt.lua is mine.

This seems to happen most often when I've just re-logged in after having screen saver on. I can't seem to manually reproduce it yet.