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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def field_values(self):
 """ Access the field_values :returns: twilio.rest.autopilot.v1.assistant.field_type.field_value.FieldValueList :rtype: twilio.rest.autopilot.v1.assistant.field_type.field_value.FieldValueList """

        if self._field_values is None:
            self._field_values = FieldValueList(
                self._version,
                assistant_sid=self._solution['assistant_sid'],
                field_type_sid=self._solution['sid'],
            )
        return self._field_values