Attempting to return null in a custom function that has GameObject as an example set as the return type will log the error:
(Execution Failure Error)</b>: Return Value is not of expected type 'GameObject'.
I would expect a FC custom function to be able to return null if the return type is set to a class like in any C# function.

Attached image is just an example off what can cause the error.

This makes making custom functions that for example search for things annoying to do since they must return a valid value.