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', '174n0m8hc28dj4rb99a0qokvr4', '216.73.216.147', '1751759766', '1751759766', '/product_info.php?info=p17_20-Tissue-Napkins.html&XTCsid=f6e58886be8011b1d9a8e232c116cb7a')

[XT SQL Error]