fuel/core — pull request #1344 by indigofeather (2013-02-19 13:30:22+00:00)
Title: Fixed Event_Instance::unregister()

The annotation in 2nd param is null for all.
```php
/**
* Unregister/remove one or all callbacks from event
*
* @param string $event event to remove from
* @param mixed $callback callback to remove [optional, null for all]
* @return boolean wether one or all callbacks have been removed
*/
```

But in condition is true