Counterbalancing with shelf

Hello

Description of the problem:
I try to use the new shelf feature to counter-balance two groups. An error message keeps popping up which I find distracting and I wonder what I might be doing wrong. I am using PsychoPy 2022.2.4.

The error message is:
Alert 4210: JavaScript Syntax Error in ‘Begin JS Experiment’ tab. See ‘Line 11: Unexpected identifier’ in the ‘Begin JS Experiment’ tab.
For more info see https://docs.psychopy.org/alerts/4210.htmlAlert 4210: JavaScript Syntax Error in ‘Begin JS Experiment’ tab. See ‘Line 11: Unexpected identifier’ in the ‘Begin JS Experiment’ tab.

Here my JS-only code component with the relevant line.

The shelf element looks like this

What causes the syntax error?

Thanks for your help in advance Jens