1366 - Incorrect integer value: '' for column 'customer_id' at row 1

insert into whos_online (customer_id, full_name, session_id, ip_address, time_entry, time_last_click, last_page_url) values ('', 'Guest', 'cnkmfvubm15gtdep8he62ud1t1', '216.73.216.244', '1752207649', '1752207649', '/index.php?cat=c4_Beer-Mugs.html&XTCsid=a63f52844b6e675f480eaf86612536c2')

[XT SQL Error]