public function getFirstError(string $key, string $group = null)
    {
        if (!empty($group)) {
            if (isset($this->errors[$group][$key])) {
                $first = array_slice($this->errors[$group][$key], 0, 1);

                return array_shift($first);
            }
        }

        if (isset($this->errors[$key])) {
            $first = array_slice($this->errors[$key], 0, 1);

            return array_shift($first);
        }

        return '';
    }