code: func (ec *Client) StorageAt(ctx context.Context, account common.Address, key common.Hash, blockNumber *big.Int) ([]byte, error) {
  	var result hexutil.Bytes
  	err := ec.c.CallContext(ctx, &result, "eth_getStorageAt", account, key, toBlockNumArg(blockNumber))
  	return result, err
  }
docs: // StorageAt returns the value of key in the contract storage of the given account.
  // The block number can be nil, in which case the value is taken from the latest known block.