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', 't377tq8h8eu32aokt26h1sgdh1', '216.73.216.244', '1752203959', '1752203959', '/index.php?XTCsid=a3b8bf2959b629f4e700fd83d8e68631')

[XT SQL Error]