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', 'd9u048nf5sg0igqts7g65vkn66', '216.73.216.80', '1751324091', '1751324091', '/index.php?cat=c4_Beer-Mugs.html&XTCsid=72205775904d1a5c41b590dd7b5ff1d6')

[XT SQL Error]