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', '8gqnq6iq9rri1er8u4g2kd1pr1', '107.22.127.78', '1493220863', '1493220863', '/shop_content.php?coID=7')

[XT SQL Error]