Add a `whereNull()` or a `nullsCount` to iterable extension

[Valentin Vignal]

It would be useful to know the number of null in an iterable. For now, I'm creating my own.

extension on Iterable {
  int nullsCount => where((element) => element == null).length;
}

[Philip]

Feels like this functionality is very specific to your projects business logic and not so much a general one.