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', 's9bl2d9ger7tqc28ui5sohq8u0', '216.73.217.32', '1791390800', '1791390800', '/index.php?XTCsid=502c4d4f7753d1888d9a6ca985d5c9c9&cat=c4_Beer-Mugs.html')

[XT SQL Error]