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', '8uns1e0mbk0m94cdqm51sslhh2', '54.162.109.90', '1495804054', '1495804054', '/product_info.php?info=p131_Cartoon-T-Shirt.html&cartoon=880')

[XT SQL Error]