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', 'vbr0fea97dah5o9jn8vn1k7dj7', '107.22.127.78', '1493220728', '1493220728', '/product_info.php?info=p720_Schoene-Toechter.html')

[XT SQL Error]