protected function verifyExtras(array $extras)
    {
        if (!isset($extras['php-env-builder'])) {
            throw new \InvalidArgumentException(
                'The parameter handler needs to be configured through the ' .
                'extra.php-env-builder setting.'
            );
        }

        if (!is_array($extras['php-env-builder'])) {
            throw new \InvalidArgumentException(
                'The extra.php-env-builder setting must be an array or a configuration object.'
            );
        }

        if (!isset($extras['php-env-builder']['questions']) || !is_array($extras['php-env-builder']['questions'])) {
            throw new \InvalidArgumentException(
                'The extra.php-env-builder.questions setting must be an array of questions.'
            );
        }
    }