Issue with void-obj of Test Thing

I have noticed a weird behavior with test thing. I have taken the td at http://plugfest.thingweb.io:8083/testthing and generated the flow. Everything but the following actions work: `int-void`, `int-int`, `int-string`. For those ones, I get nothing displayed on the UI but the flow editor shows internal server error. Sending the same request on postman, for example for `int-int` with input 12 returns 13. Action `void-obj` does exactly what I expect.

The error is `Error: Server error: Internal Server Error`

_Originally posted by @egekorkan in https://github.com/eclipse-thingweb/node-red/issues/25#issuecomment-2125677188_