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', '49nn1beqdis7v9dgf5b7nk5v51', '54.196.107.247', '1495571275', '1495571275', '/product_info.php?info=p15_NICHTWEIHNACHTEN.html&refID=nlrss')

[XT SQL Error]