private function getDefaultNormalizer()
    {
        $default = $this->getDefault();
        $trueRegex = $this->trueAnswerRegex;
        $falseRegex = $this->falseAnswerRegex;

        return function ($answer) use ($default, $trueRegex, $falseRegex) {
            if (is_bool($answer)) {
                return $answer;
            }
            if (empty($answer) && !empty($default)) {
                return $default;
            }

            if (preg_match($trueRegex, $answer)) {
                return true;
            }

            if (preg_match($falseRegex, $answer)) {
                return false;
            }

            return null;
        };
    }