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

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

will work. That's because there is no conversion from the type of the first expression (null) to the type of the second expression (double).