WebChannel behavoir change in 5.12

I started a project using QWebEngine with 5.12.0. I recently upgraded to 5.12.5/5.12.6 and noticed that some of the QWebChannel functionality that I use, changed.

I tried making a minimal example, which show the problem.
I also uploaded the code here: https://github.com/tnixeu/QWebChannelBug
You can download it also here: https://github.com/tnixeu/QWebChannelBug/archive/master.zip

The first screenshot is done when using Qt 5.12.0. The second one is using 5.12.6.

Since at least 5.12.5 I get an array containing "null" values instead of the correct data.