This code is throwing not supported between instances of NoneType and NoneType error How can Fix this

Question

def summary(self, request, url_view_detail):

        def status(data):

            if data['status'] is not None:

                if data['expired_at'] < data['started_at']:

                    return contribution_status_display(3, True)

                else:    

                    return contribution_status_display(data['status'], True)

            else:

                return 'not available'