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', 'mkqqcjfa0uvf4fmatnp76pi8i1', '216.73.216.9', '1757806211', '1757806211', '/index.php?XTCsid=61ba925c46144fb6a3eaf868339da23b')

[XT SQL Error]