Flask query result is none but if statements not working properly

Question

I don't have any row in my table and I expect that model query return None. So far everything is normal. But in following code, else statement works. I would like to know why else statement is working even though it is None.

known_dataset = Dataset.query.filter_by(user_id=current_user, status='1').first()
print('====known_dataset', known_dataset) # <Dataset None>
if known_dataset is None:
     print('====if') # not working
     known_dataset = Dataset()
     ...
else:
     print('====else') # working
     ...