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', 'a66ff19cb6d2b6ea52d7dfb712a2bf3d', '216.73.216.140', '1775894178', '1775894178', '/shop/index.php')

[XT SQL Error]