Null and wrong parameter in front of the operation

I would like to give some feedback about ...

From: https://checkio.org/mission/boolean-algebra/solve/

HTTP_USER_AGENT:

Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Firefox/45.0

I tried this code in pycharm and it worked, but on here is says null and has a u in front of the operation name.