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.

Your link doesn’t work! 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.