<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _add_updated_at_column(self, values):
 """ Add the "updated_at" column to a dictionary of values. :param values: The values to update :type values: dict :return: The new dictionary of values :rtype: dict """

        if not self._model.uses_timestamps():
            return values

        column = self._model.get_updated_at_column()

        if "updated_at" not in values:
            values.update({column: self._model.fresh_timestamp_string()})

        return values