An event with Soft Class Reference as an input that is not set causes package to fail with Nativization

Having a custom event with an empty Soft Class Reference as an input causes packaging to fail if nativization is enabled as the event nativizes with a const TSoftClassPtr<>& and the compiler cannot convert a temporary nullptr to a reference.

Regression?: No
This occurs in 4.18 and 4.19

1. Create a new project
2. Create a new Blueprint
3. Add a new custom event
4. Add an Actor > Soft Class Reference as an input
5. Call the event on BeginPlay
6. Add an instance of the Blueprint to the level
7. Save the map
8. Add the map as the default game map
9. Enable Inclusive Nativization
10. Package for Win64
    Result: Packaging fails due to the event nativizing with a const TSoftClassPtr<>& and the compiler cannot convert a temporary nullptr to a reference
    Expected: Packaging succeeds