whereNotNull method
The non-null elements of this Iterable.
Returns an iterable which emits all the non-null elements
of this iterable, in their original iteration order.
For an Iterable<X?>, this method is equivalent to .whereType<X>().
Implementation
@Deprecated('Use .nonNulls instead.')
Iterable<T> whereNotNull() sync* {
  for (var element in this) {
    if (element != null) yield element;
  }
}