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', '4s1tuuct59u8vc0g3l00nck571', '216.73.216.9', '1758199167', '1758199167', '/product_info.php?XTCsid=a6fef95dcbdcf765a3c6baf6e1fe0e25&info=p15_25-balloons.html&language=de')

[XT SQL Error]