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', '556a319ed836758b6e6c504f1e69f204', '216.73.216.38', '1776418408', '1776418408', '/shop/product_info.php?info=p138_.html')

[XT SQL Error]