code: def validate(self, data):
          
          time = timezone.now()
          status_type = data.pop('status_type')
          if status_type == 'Interim-Update':
              data['update_time'] = time
          if status_type == 'Stop':
              data['update_time'] = time
              data['stop_time'] = time
          return data
docs: We need to set some timestamps according to the accounting packet type
          * update_time: set everytime a Interim-Update / Stop packet is received
          * stop_time: set everytime a Stop packet is received
          * session_time: calculated if not present in the accounting packet
          :param data: accounting packet
          :return: Dict accounting packet