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', '4d9u2goa9qif5m793mlcfmvds3', '216.73.216.160', '1757270821', '1757270821', '/xtshop/index.php?cat=c1_FOLIEN.html')

[XT SQL Error]