Setter dependencies are optional. Their types should have a Null Object pattern implementation, and if not it's often a good idea to decorate them with one. For example, if an optional dependency hasn't been set, it might not be desirable to have a null reference exception when a method is invoked on it
The challenge is to provide a facility for Windsor that will detect an optional dependency and fill it with a Null Object (i.e, an implementation that doesn't do anything). It is safe to assume that all such dependencies are using interfaces.
Can you do it?