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', 'a8bcdf50b63b6dcdeecfc2fcf65d3a2d', '34.229.24.100', '1563487431', '1563487431', '/shop_content.php/coID/6/product/Gutscheine')

[XT SQL Error]