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', '8gll9bh5p5elqqrnp76vrvsi54', '216.73.216.140', '1763568434', '1763568434', '/shop_content.php?XTCsid=75dc59d6a30660e0992222d2318ca53e&coID=4&language=de')

[XT SQL Error]