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', '4gjmft92ps1rrqs2qpmv763f41', '216.73.216.176', '1762309207', '1762309207', '/product_info.php?XTCsid=a6fef95dcbdcf765a3c6baf6e1fe0e25&info=p15_25-balloons.html&language=de')

[XT SQL Error]