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', 'kci904p69rflluvfeajm1cu9l6', '216.73.216.147', '1751760588', '1751760588', '/product_info.php?info=p2_Bavarian-Pennant-Chain.html&XTCsid=15cbbc13723f7bc63afaf1294f637517')

[XT SQL Error]