XML Conversion results in </>

Hello @soldair , 
at the moment I am having issues to convert a json string into xml.
It results in a string like this </></></>
I have added you to my Gitlab Repo. This contains the example where it results in this output.

check the variable output_group.

Would be great to find a reason why it does this. 

Thankyou and Best Regards

Kaliph