Differences between decltype(void()) and decltype(void{})

This is a follow-up of the question: What does the void() in decltype(void()) mean exactly?.

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decltype(void()) compiles fine and what the void() means in this case is explained in the above mentioned question (actually in the answer).
On the other side, I noticed that decltype(void{}) doesn't compile.

What's the difference between them (in the context of a decltype at least)?
Why doesn't the second expression compile?

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For completeness, it follows a minimal (not-)working example:

int main() {
    // this doesn't compile
    //decltype(void{}) *ptr = nullptr;
    // this compiles fine
    decltype(void()) *ptr = nullptr;
    (void)ptr;
}