code: func (api *PrivateDebugAPI) StorageRangeAt(ctx context.Context, blockHash common.Hash, txIndex int, contractAddress common.Address, keyStart hexutil.Bytes, maxResult int) (StorageRangeResult, error) {
  	_, _, statedb, err := api.computeTxEnv(blockHash, txIndex, 0)
  	if err != nil {
  		return StorageRangeResult{}, err
  	}
  	st := statedb.StorageTrie(contractAddress)
  	if st == nil {
  		return StorageRangeResult{}, fmt.Errorf("account %x doesn't exist", contractAddress)
  	}
  	return storageRangeAt(st, keyStart, maxResult)
  }
docs: // StorageRangeAt returns the storage at the given block height and transaction index.