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', '51002aa673ba64550e855bcaafd6194d', '216.73.216.42', '1763354820', '1763354820', '/shop/product_info.php?info=p156_.html')

[XT SQL Error]