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', '9thr56aairovimve2vn5jur534', '216.73.216.139', '1770818526', '1770818526', '/index.php?XTCsid=df3729dd436fcb28ea9e03ba06716f33')

[XT SQL Error]