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', 'd5uf1tr0lmvi7cddd04kd0pb36', '216.73.217.92', '1781008157', '1781008157', '/xtshop/index.php')

[XT SQL Error]