code: func (l *kvLedger) GetPvtDataByNum(blockNum uint64, filter ledger.PvtNsCollFilter) ([]*ledger.TxPvtData, error) {
  	pvtdata, err := l.blockStore.GetPvtDataByNum(blockNum, filter)
  	l.blockAPIsRWLock.RLock()
  	l.blockAPIsRWLock.RUnlock()
  	return pvtdata, err
  }
docs: // GetPvtDataByNum returns only the pvt data  corresponding to the given block number
  // The pvt data is filtered by the list of 'collections' supplied