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', '7559f21ekmen9698c1o3gi8ld2', '216.73.216.9', '1758139314', '1758139314', '/index.php?XTCsid=792dd2eece839333bab562194e3fb545&cat=c6_Foodstuffs.html')

[XT SQL Error]