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', 'pev2e99cqo2pdbemc8icli6d30', '216.73.216.180', '1766725735', '1766725735', '/index.php?XTCsid=7c604026da355cfd6a094c68b431572d&language=en')

[XT SQL Error]