protected function jsonDecode(Field $f, $value, $assoc = true)
    {
        // constant supported only starting PHP 7.3
        if (!defined('JSON_THROW_ON_ERROR')) {
            define('JSON_THROW_ON_ERROR', 0);
        }

        $res = json_decode($value, $assoc, 512, JSON_THROW_ON_ERROR);
        if (JSON_THROW_ON_ERROR == 0 && json_last_error() !== JSON_ERROR_NONE) {
            throw new Exception([
                'There was error while decoding JSON',
                'code'  => json_last_error(),
                'error' => json_last_error_msg(),
            ]);
        }

        return $res;
    }