How to make no response a wrong response

URL of experiment: Pavlovia

Description of the problem:

For the practice part, when there isn’t any key pressed, the feedback is the same as if you press the wrong one. I can implement this in the builder, but when pushed online, it will report an error.

Then I modified the auto-generated javascript code.
Change the “key_resp_2.keys=undefined” to “key_resp_2.keys =”.
Still exist other errors. Hope there is a better way to fix this.