code: func (ec *Client) NonceAt(ctx context.Context, account common.Address, blockNumber *big.Int) (uint64, error) {
  	var result hexutil.Uint64
  	err := ec.c.CallContext(ctx, &result, "eth_getTransactionCount", account, toBlockNumArg(blockNumber))
  	return uint64(result), err
  }
docs: // NonceAt returns the account nonce of the given account.
  // The block number can be nil, in which case the nonce is taken from the latest known block.