code: func (s *Store) GetPvtDataByNum(blockNum uint64, filter ledger.PvtNsCollFilter) ([]*ledger.TxPvtData, error) {
  	s.rwlock.RLock()
  	defer s.rwlock.RUnlock()
  	return s.getPvtDataByNumWithoutLock(blockNum, filter)
  }
docs: // GetPvtDataByNum returns only the pvt data  corresponding to the given block number
  // The pvt data is filtered by the list of 'ns/collections' supplied in the filter
  // A nil filter does not filter any results