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', '21c4514ab58cc14368cae2792e3bdbae', '216.73.216.169', '1755543476', '1755543476', '/shop/product_info.php?info=p110_.html')

[XT SQL Error]