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', 'bqp0ts9q4q7gbgo14nkcau2ls1', '216.73.216.244', '1752209480', '1752209480', '/index.php?language=de&XTCsid=1455d70b156c4853db961f68b595bbe7')

[XT SQL Error]