Database Error

A database error occurred while performing the requested procedure. Please review the database error below for more information.

There was an SQL error: Column 'userid' cannot be null - INSERT INTO `user_friends` (`userid`, `friendid`, `status`) VALUES (NULL, '2189', NULL)

Error occurred at line 414 of system/libraries/drivers/Database_Mysql.php.

Loaded in 0.0492 seconds, using 1.53MB of memory. Generated by Kohana v2.0.