How to set focus to Object Reference in Task Blueprint (AI)

My problems are set focus zombie to Target, the target is the blackboard key type Object Reference - Actor. When I get the value that key to set focus, It said only support for the actor, Target key is Object Reference. So how I can set focus or any way to convert Object reference to Actor (I don’t want to use "Cast to … " Because of the target not only 1 blueprint.)