public NumberDigitizer digitizerBy(final Integer aNumber) {
        if (aNumber == null) {
            throw new NonDigitizableNumberException("The number to conversion is null");
        }
        if (aNumber < 0) {
            throw new NonDigitizableNumberException("The number to convert is negative");
        }
        if (aNumber > 9) {
            throw new NonDigitizableNumberException("The number to convert is greater than 9");
        }
        return digits[aNumber];
    }