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', 'a9aad61drq536h9m5scf2ma6a4', '216.73.217.60', '1778631485', '1778631485', '/xtshop/index.php?cat=c103_.html')

[XT SQL Error]