Assign default actor to blueprint

Hello friends,

I have a blueprint where it has default value for the actor ref.But when i try to put the reference it says

LogProperty:Warning: Illegal TEXT reference to a private object in external package.Import failed…

But when i place that blueprint in the scene i will be able to assign the ref to actor.Is this a bug or am i doing something wrong.

What if i want to assign the def actor in the blueprint itself instead of dragging it to the scene and assigning it.