docs: def __update(self, task_source):
  		""" Recheck next start of tasks from the given one only
  
  		:param task_source: source to check
  
  		:return: None
  		"""
  		next_start = task_source.next_start()
  		if next_start is not None:
  
  			if next_start.tzinfo is None or next_start.tzinfo != timezone.utc:
  				raise ValueError('Invalid timezone information')
  
  			if self.__next_start is None or next_start < self.__next_start:
  				self.__next_start = next_start
  				self.__next_sources = [task_source]
  			elif next_start == self.__next_start:
  				self.__next_sources.append(task_source)