Trengginas Cahyo Putro

Hi i have DaloRadius with freeradius 3, php v4.1, on ubuntu server, the web server path /var/www/html/daloradius. the php-gd are installed. and all chart is blank or empty, im check error log on apache2.log bellow. i hope some help for this error, thank you... " Unsupported operand types: string - null in /var/www/html/daloradius/include/management/userReports.php:386\nStack trace:\n#0 /var/www/html/daloradius/mng-edit.php(1110): userPlanInformation()\n#1 {main}\n thrown in /var/www/html/daloradius/include/management/userReports.php...