Ha ocurrido un error con la base de datos

Error Number: 1048

Column 'agent' cannot be null

INSERT INTO `site_public_tracking` (`ipaddress`, `targetpage`, `isBot`, `isPhone`, `isComputer`, `operatingSystem`, `isReferred`, `referral`, `agent`, `browserVersion`) VALUES ('3.235.145.95', 'courses/public_courses/courseSignup/16', 0, 0, 0, 'Unknown Platform', 0, 'None', NULL, '')

Filename: libraries/Visitor_tracker.php

Line Number: 81