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', '1gp2mk9ma424t2jotl8vghhbs4', '216.73.216.28', '1775704519', '1775704519', '/index.php?XTCsid=d3edd3fcb58e1977f2007b47233256d4')

[XT SQL Error]