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', '9hs8rdjlpn8a0np6u85ffboa63', '216.73.216.9', '1758155343', '1758155343', '/index.php?XTCsid=0832187515ca706758d8e1ce01e34faf&cat=c4_Beer-Mugs.html')

[XT SQL Error]