c++ - Why doesn't void{} exist?

Question

I am wondering why void() is a prvalue of void but void{} does not exist...? See the following answer: https://stackoverflow.com/a/37708167/293195

For example in the context:

template<typename R>
R foo(){
 return R{};
}

Answer 1

CWG 2351, resolved in June, has made void{} legal.