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', 'r4u7jkckk7h0ocsn6ra3kn3le2', '216.73.216.36', '1773810979', '1773810979', '/xtshop/index.php?cat=c43_.html')

[XT SQL Error]