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', 'bnu9efn5dg6tr4fnb9l08flph2', '54.196.107.247', '1495571521', '1495571521', '/checkout_shipping.php')

[XT SQL Error]