code: func (l *kvLedger) GetBlockByNumber(blockNumber uint64) (*common.Block, error) {
  	block, err := l.blockStore.RetrieveBlockByNumber(blockNumber)
  	l.blockAPIsRWLock.RLock()
  	l.blockAPIsRWLock.RUnlock()
  	return block, err
  }
docs: // GetBlockByNumber returns block at a given height
  // blockNumber of  math.MaxUint64 will return last block