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', '4nijt8731si8pdtptha10eoed2', '216.73.217.128', '1788231494', '1788231494', '/index.php?XTCsid=38f09672db884903e3803adf9d076819&language=de')

[XT SQL Error]