code: func (ec *EthereumClient) GetStorageAt(ctx *Context, account *Address, key *Hash, number int64) (storage []byte, _ error) {
  	if number < 0 {
  		return ec.client.StorageAt(ctx.context, account.address, key.hash, nil)
  	}
  	return ec.client.StorageAt(ctx.context, account.address, key.hash, big.NewInt(number))
  }
docs: // GetStorageAt returns the value of key in the contract storage of the given account.
  // The block number can be <0, in which case the value is taken from the latest known block.