anchor.diff:  
   bool _areArgumentsSubtypes(Object? universe, Object? sArgs, Object? sVariances,
       Object? sEnv, Object? tArgs, Object? tEnv) {
  -  int length = sArgs != null ? _Utils.arrayLength(sArgs) : 0;
  +  int length = _Utils.arrayLength(sArgs);
     assert(length == _Utils.arrayLength(tArgs));
     bool hasVariances = sVariances != null;
     if (JS_GET_FLAG("VARIANCE")) {
  
positive.code:   bool changed = false;
    int length = _Utils.arrayLength(namedArray);
    assert(_Utils.isMultipleOf(length, 3));
    Object? result = JS('', '[]');
    for (int i = 0; i < length; i += 3) {
      String name = _Utils.asString(_Utils.arrayAt(namedArray, i));
      bool isRequired = _Utils.asBool(_Utils.arrayAt(namedArray, i + 1));
  
negative.code:     if (normalize) {
        int length = _Utils.arrayLength(bounds);
        int count = 0;
        Object? typeArguments = _Utils.newArrayOrEmpty(length);
        for (int i = 0; i < length; i++) {
          Rti bound = _Utils.asRti(_Utils.arrayAt(bounds, i));
          if (Rti._getKind(bound) == Rti.kindNever) {
  