code: func (w *wizard) readDefaultBigInt(def *big.Int) *big.Int {
  	for {
  		fmt.Printf("> ")
  		text, err := w.in.ReadString('\n')
  		if err != nil {
  			log.Crit("Failed to read user input", "err", err)
  		}
  		if text = strings.TrimSpace(text); text == "" {
  			return def
  		}
  		val, ok := new(big.Int).SetString(text, 0)
  		if !ok {
  			log.Error("Invalid input, expected big integer")
  			continue
  		}
  		return val
  	}
  }
docs: // readDefaultBigInt reads a single line from stdin, trimming if from spaces,
  // enforcing it to parse into a big integer. If an empty line is entered, the
  // default value is returned.