Hello @perelin!
Very odd bug, I believe it must be a linting error on our end. I cloned your app, saw the same error and was not able to figure out where it is coming from or why it is showing up 
I will send it to our eng team to see if they can get to the bottom of it. For now, I would not worry. As you said, everything is working.
If the error is blocking you in any way, let me know and I can add in more details to the bug ticket!