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', 'gsivpbtkkcav3r9qij230h78k1', '34.229.76.193', '1558616740', '1558616740', '/index.php?language=de')

[XT SQL Error]