<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def map_column(self, value):
 """ Applied to each column of every row returned by `rows`. Default behaviour is to escape special characters and identify any self.null_values. """

        if value in self.null_values:
            return r'\\N'
        else:
            return default_escape(six.text_type(value))