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', 'e7ohsgak9enldvncpf46q613m4', '216.73.216.244', '1752201339', '1752201339', '/index.php?cat=c4_Beer-Mugs.html&XTCsid=d163dd0fc0b54bf3066f85422c77e00a')

[XT SQL Error]