anchor.diff:      // with filled-in type arguments.
   
       if (callSelectors != null) {
  -      Set<ParameterStructure> parameterStructures;
  +      Set<ParameterStructure>? parameterStructures;
         for (Selector selector in callSelectors.keys) {
           CallStructure callStructure = selector.callStructure;
           if (callStructure.typeArgumentCount != 0) continue;
  
positive.code: // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
  // for details. All rights reserved. Use of this source code is governed by a
  // BSD-style license that can be found in the LICENSE file.
  
  // @dart = 2.10
  
  library dart2js.js_emitter.instantiation_stub_generator;
  
  
negative.code:     assert(typeArgumentCount > 0);
  
      // 2. Find the function field access path.
      late FieldEntity functionField;
      _elementEnvironment.forEachInstanceField(instantiationClass,
          (ClassEntity enclosing, FieldEntity field) {
        if (_closedWorld.fieldAnalysis.getFieldData(field as JField).isElided)
          return;
        if (field.name == '_genericClosure') functionField = field;
      });
  
      String call = _namer.closureInvocationSelectorName;
      Map<Selector, SelectorConstraints>? callSelectors =
          _codegenWorld.invocationsByName(call);
  
      Set<ParameterStructure> computeLiveParameterStructures() {
  