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', 'an9fage5l88qe4pd4fv002abv2', '216.73.216.128', '1764838102', '1764838102', '/xtshop/index.php?cat=c63_.html')

[XT SQL Error]