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', '5mk64o42o0qp74262308apba90', '3.80.128.196', '1555648611', '1555648611', '/shop/index.php?language=de&cat=c53_Guide-Line---Power-Taper.html&XTCsid=5mk64o42o0qp74262308apba90')

[XT SQL Error]