Zapier Python editor doesn't output anything even though code works in python

I'm trying to create code that matches True/False messages from checkboxes from a form to the checkbox titles. Whenever the checkboxes are clicked, the titles should be appended to a list that is outputted in the end.

This is my code:

def nische(input_data):
nischen = []
for key in input_data:
    if input_data[key] == True:
        print(key)
        nischen.append(key)
if input_data['Sonstiges'] != "":
    nischen.append(input_data['Sonstiges'])
string = ', '.join(nischen)
string = str(string)
return string

result = nische(input_data) output = print(result)

​I've tried everything, but the Zapier Interpreter shows no output.

this is the zapier output enter image description here ​ ​

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