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', '3u388th5l296nm29085oavd5m4', '216.73.216.159', '1767883959', '1767883959', '/xtshop/index.php?cat=c15_.html')

[XT SQL Error]