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', '4lg5pq1r8qfu992las5ustcm47', '216.73.216.9', '1757979116', '1757979116', '/index.php?XTCsid=69a1e06b1d537d651878c63fe4ee3fec&cat=c4_Beer-Mugs.html')

[XT SQL Error]