Hi @Pascal Lammers 

Good question.

We’d need a full screenshot of the input values sent as part of the DATA IN for the Code step.

(scroll down and take a screenshot)

If the value can be null, then you may have to add additional logic to handle that data use case.

Here are the screenshots of the Input Data

I don’t know why I’m getting the error, because in the Editor everything is working fine. 

Thanks for getting back @Troy Tessalone 

@Pascal Lammers 

In this example, there was no value provided for “articlenumber”, hence the error.

Check your previous Zap step (3) to see the DATA OUT since the output is mapped to the Code step.

Thanks for getting back! 
My fault ‍♂️ - just checked the Zap and I had one Input wrong

Lesson learned - @Troy Tessalone