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', '021j4megsv1b5ab2pro8h17k15', '216.73.216.102', '1778725016', '1778725016', '/xtshop/product_info.php?info=p969_.html')

[XT SQL Error]