anchor.diff:  }
   
   // Internal helper to populate a [multimap] from an [Iterable].
  -void fillFromIterable<K, V, VS extends Iterable<V>>(Multimap<K, V, VS> multimap,
  -    Iterable iterable,
  -    // ignore: use_function_type_syntax_for_parameters, type_annotate_public_apis
  -    K key(element),
  -    // ignore: use_function_type_syntax_for_parameters, type_annotate_public_apis
  -    V value(element),) {
  +void fillFromIterable<K, V, VS extends Iterable<V>>(
  +  Multimap<K, V, VS> multimap,
  +  Iterable iterable,
  +  // ignore: use_function_type_syntax_for_parameters, type_annotate_public_apis
  +  K key(element),
  +  // ignore: use_function_type_syntax_for_parameters, type_annotate_public_apis
  +  V value(element),
  +) {
     key ??= (x) => x;
     value ??= (x) => x;
     for (final element in iterable) {
  
positive.code:   VS operator [](Object key) => _multimap[key];
  
    @override
    void operator []=(K key, VS value) =>
        _multimap.replaceAll(key, value);
  
    @override
    void clear() => _multimap.clear();
  
negative.code: }
  
  // Internal helper to populate a [multimap] from an [Iterable] of entries.
  void fillFromEntries<K, V, VS extends Iterable<V>>(
      Multimap<K, V, VS> multimap, Iterable<MapEntry<K, V>> entries) {
    for (final entry in entries) {
      multimap.add(entry.key, entry.value);
    }
  