Why dart optional named argument is not null if not provided?

Question

When optional named parameter is not provided, why it is not null as expected?

void main() {
  num double({v: num}) {
    if (v == null)
      return 0;
    else
      return v * 2;
  }

  print(double(v: 2));
  print(double());
  print('done');
}

which output as

4
Uncaught TypeError: v.$mul is not a function

Answer 1

num double({v: num}) {

defines a named parameter v of type dynamic with the default value num (a type)

It should instead be

num double({num v}) {

to make your code work as expected