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', '2vdmfvo33p16kqmsj0dv622236', '216.73.216.244', '1752216382', '1752216382', '/product_info.php?language=de&info=p12_33-feet-crape-paper.html&XTCsid=cdfc0f2ea8be6cebe1f6056b0a37d83f')

[XT SQL Error]