Database error in vBulletin 3.8.5:

Invalid SQL:

        UPDATE cron
        SET nextrun = 1276988400
        WHERE cronid = 27 AND nextrun =;

MySQL Error   : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 3
Error Number  : 1064
Request Date  : Saturday, June 19th 2010 @ 04:09:02 AM
Error Date    : Saturday, June 19th 2010 @ 04:09:06 AM
Script        : http://www.example.com/vb/admincp/plugin.php?do=productimport
Referrer      : http://www.example.com/vb/admincp/plugin.php?do=productadd
IP Address    : xx.xx.xx.xx
Username      : xxxxx
Classname     : vB_Database
MySQL Version : 5.0.90-community

// save it
        $vbulletin->db->query_write("
                UPDATE " . TABLE_PREFIX . "cron
                SET nextrun = " .  $nextrun . "
                WHERE cronid = " . intval($cronid) . " AND nextrun = " . $crondata['nextrun']
        );

// save it
        $vbulletin->db->query_write("
                UPDATE " . TABLE_PREFIX . "cron
                SET nextrun = " .  $nextrun . "
                WHERE cronid = " . intval($cronid)
        );