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', '9tv5nisc5i7vgrv4ddn7lf7jl0', '216.73.216.179', '1792893230', '1792893230', '/xtshop/shop_content.php?coID=1')

[XT SQL Error]