Crash when testing the experimental blur effect on themes

Distribution

Mint 21.2

Package version

Cinnamon 5.8.4

Graphics hardware in use

No response

Frequency

Always

Bug description

I've been testing the experimental blur effect a bit and it worked well for most of the places I applied it:

The only place I had a problem was when trying to apply the blur effect with the component with the #overview id:

Then Cinnamon would crash when trying to access the scale/overview mode.

Steps to reproduce

Add a background blur effect to #overview in cinnamon.css, reload Cinnamon, and try to open the scale view, Cinnamon will probably crash.

Expected behavior

Cinnamon should not crash even if it is not expected to be applied a background blur effect to that component.

Additional information

1. Crash Trace ==> https://termbin.com/vj4j
2. I tested the blur effect with the CBlack theme, that can be installed in the theme settings.

Start by reproducing the crash after adding a background blur effect to #overview in cinnamon.css and opening scale/overview mode. Read the linked crash trace and trace the affected overview code. Done means Cinnamon no longer crashes when this blur effect is applied, including when the effect is unsupported for that component.