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', 'c8uk3ujvcjt5eao3hlj5kv6ve3', '216.73.216.147', '1751962640', '1751962640', '/index.php?cat=c4_Beer-Mugs.html&XTCsid=792dd2eece839333bab562194e3fb545')

[XT SQL Error]