anchor.diff:      int length = JS('', '#.size', map);
       other.forEach((K key, V value) {
         if (key == null) {
  -        JS('', '# = null', key);
  +        key = JS('', 'null');
         } else if (JS<bool>('!', '#[#] !== #', key,
             dart.extensionSymbol('_equals'), dart.identityEquals)) {
           key = putLinkedMapKey(key, _keyMap);
  
positive.code:   V putIfAbsent(K key, V ifAbsent()) {
      var map = _map;
      if (key == null) {
        JS('', '# = null', key);
        if (JS<bool>('!', '#.has(null)', map)) return JS('', '#.get(null)', map);
      } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
          dart.identityEquals)) {
  
negative.code: 
    V? remove(Object? key) {
      if (key == null) {
        key = JS('', 'null');
      } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
          dart.identityEquals)) {
        @notNull
  