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', '08rcdadnm7g88kdde6lbho4e31', '216.73.217.114', '1781097826', '1781097826', '/index.php?XTCsid=7a53dc57544f424e178883984417ebd9&language=de')

[XT SQL Error]