升级wordpress核心后，php 7.1中出现非数字值错误

i have this error after upgrade to php 7.1 and update wordpress core:

PHP Warning: A non-numeric value encountered in /wp-includes/SimplePie/Parse/Date.php on line 694

here the code of that file

    public function date_w3cdtf($date)
{
    static $pcre;
    if (!$pcre)
    {
        $year = '([0-9]{4})';
        $month = $day = $hour = $minute = $second = '([0-9]{2})';
        $decimal = '([0-9]*)';
        $zone = '(?:(Z)|([+\-])([0-9]{1,2}):?([0-9]{1,2}))';
        $pcre = '/^' . $year . '(?:-?' . $month . '(?:-?' . $day . '(?:[Tt\x09\x20]+' . $hour . '(?::?' . $minute . '(?::?' . $second . '(?:.' . $decimal . ')?)?)?' . $zone . ')?)?)?$/';
    }
    if (preg_match($pcre, $date, $match))
    {
        /*
        Capturing subpatterns:
        1: Year
        2: Month
        3: Day
        4: Hour
        5: Minute
        6: Second
        7: Decimal fraction of a second
        8: Zulu
        9: Timezone ±
        10: Timezone hours
        11: Timezone minutes
        */

        // Fill in empty matches
        for ($i = count($match); $i <= 3; $i++)
        {
            $match[$i] = '1';
        }

        for ($i = count($match); $i <= 7; $i++)
        {
            $match[$i] = '0';
        }

        // Numeric timezone
        if (isset($match[9]) && $match[9] !== '')
        {
            $timezone = $match[10] * 3600;
            $timezone += $match[11] * 60;
            if ($match[9] === '-')
            {
                $timezone = 0 - $timezone;
            }
        }
        else
        {
            $timezone = 0;
        }

        // ((LINE 694))  Convert the number of seconds to an integer, taking decimals into account
        $second = round($match[6] + $match[7] / pow(10, strlen($match[7])));

        return gmmktime($match[4], $match[5], $second, $match[2], $match[3], $match[1]) - $timezone;
    }
    else
    {
        return false;
    }
}

the error is come from this line :

$second = round($match[6] + $match[7] / pow(10, strlen($match[7])));

Any ideas how to tackle this or what it is ? maybe i need to add if (is_numeric

i change that line to below and the errors gone.

$second = round((int)$match[6] + (int)$match[7] / pow(10, strlen($match[7])));