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', '4ch4tmcu1qrfbdp4254en085r0', '216.73.216.147', '1781023907', '1781023907', '/index.php?XTCsid=bdaba9e3c5005b887aab6c0c38edc3a6&language=en')

[XT SQL Error]