def check_last_dates(db):
	"""
	Check regions, that have last_date set to zero.

	:param db: instance of DatabaseQueries class <object>.
	:return: list of region ids with last_date = 0 <list> or None if empty list.
	"""
	last_dates_params = {'table': 'regions',
						  'conditions': [],
						  'condition_data': (),
						  'filters': ['id', 'last_date']}

	last_dates = db.select(**last_dates_params)

	# select zero value last_dates
	zero_last_dates = [x for x in last_dates if x[1] == 0]
	
	# if there are zero last dates return a list of ids with zero last date
	if zero_last_dates:
		return [x[0] for x in zero_last_dates]
	else:
		return None