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', '1891e2922ce985526f8b9c1092bda6da', '54.224.214.251', '1472124568', '1472124568', '/shop/product_info.php?info=p95_T-Shirt--Ich-kenn-nicht-deinen-Namen--2009.html')

[XT SQL Error]