Why doesn't this C# code compile?

Question

double? test = true ? null : 1.0;

In my book, this is the same as

if (true) {
  test = null;
} else {
  test = 1.0;
}

Answer 1

Because the compiler can't figure out that for null and 1.0 to be compatible, the values need to be cast to double?. This needs to be explicitly stated.

double? test = true ? (double?) null : 1.0;