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', 'qdqeqpf0e28ktcmk0f0q9vdcs3', '54.224.255.158', '1498515656', '1498515656', '/product_info.php?info=p639_Das-Schlaf--Hardcover-.html')

[XT SQL Error]