maxWith method
Returns the first entry having the largest value according to the provided comparator or null if there are no entries.
Implementation
MapEntry<K, V>? maxWith(Comparator<MapEntry<K, V>> comparator) {
  final i = entries.iterator;
  if (!i.moveNext()) return null;
  var max = i.current;
  while (i.moveNext()) {
    final e = i.current;
    if (comparator(max, e) < 0) {
      max = e;
    }
  }
  return max;
}