Settings form returns a string instead of an object

I am trying to customize the default content slider module of the Beaver Builder plugin. I created a new settings form but when i look at the $settings object all the data of the new settings for is stored in a single string instead of an object. I can not figure out what I did wrong. Can someone please point me in the right direction. You can find my code in the GitHub repo.

https://github.com/eliaskieser/content-slider

Your link doesn’t work!
https://kb.wpbeaverbuilder.com/article/124-custom-module-developer-guide might help you too

Thanks for your quick reply. I forgot to make the repo public but now it should work. I have already read the doc but did not find the solution. It would be great if you can have look at the code on the master branch.