firstWhereOrNull method
Implementation
T? firstWhereOrNull(bool Function(T element) test) {
  for (final element in this) {
    if (test(element)) {
      return element;
    }
  }
  return null;
}T? firstWhereOrNull(bool Function(T element) test) {
  for (final element in this) {
    if (test(element)) {
      return element;
    }
  }
  return null;
}