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