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', 't937d7f1b1f9alndq999aj1a97', '216.73.216.9', '1758058432', '1758058432', '/product_info.php?XTCsid=d6a8bfd6f6ba5ba5c5448fc18660454f&info=p16_Octoberfest-CD.html&language=de')

[XT SQL Error]