code: def diff_time(t1, t2):
      
      if t1 is None or t2 is None:
          return None
  
      if not isinstance(t1, time):
          raise ValueError('"t1" must be a datetime.time')
      if not isinstance(t2, time):
          raise ValueError('"t2" must be a datetime.time')
  
      dt1 = datetime(1, 1, 1,
                     t1.hour, t1.minute, t1.second, t1.microsecond, t1.tzinfo)
      dt2 = datetime(1, 1, 1,
                     t2.hour, t2.minute, t2.second, t2.microsecond, t2.tzinfo)
  
      return dt1 - dt2
docs: Calculates datetime.timedelta between two datetime.time values.
      :param t1: First time
      :type t1: datetime.time
      :param t2: Second time
      :type t2: datetime.time
      :return: Differences between t1 and t2 or None when t1 or t2 is None
      :rtype: datetime.timedelta/None
      :raise: ValueError when t1 or t2 is not datetime.time or None