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', 'kt0gc7nuesv612f063ou0gpuk7', '100.25.214.89', '1561369574', '1561369574', '/product_info.php?language=de&products_id=1')

[XT SQL Error]