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', '31a0fs1jgvfnid0aj70dlqh373', '216.73.216.110', '1752054374', '1752054374', '/popup_content.php?coID=1&XTCsid=38f09672db884903e3803adf9d076819')

[XT SQL Error]