Cast nodes compile without warning when no object is selected/passed in

Cast nodes compile without warning when no object is assigned to the cast nodes object input pin.

1. Open Editor (any project)
2. Open MyCharacter blueprint
3. In Eventgraph, create a "begin overlap" node.
4. Drag off of "other actor" pin, cast "other actor" to any other object
5. Remove "Other actor" input pin from "object" input pin
6. Connect exec output from event begin play to cast node
7. Compile