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', 'mddngj67mholf4dfek6u98sk20', '216.73.216.63', '1774214725', '1774214725', '/popup_content.php?XTCsid=4299a8bbf7f56cb5a06703b866244eb3&coID=1')

[XT SQL Error]