anchor.diff:  class AbstractValueFactory {
     static AbstractValue inferredReturnTypeForElement(
         FunctionEntity element, GlobalTypeInferenceResults results) {
  -    return results.resultOfMember(element).returnType ??
  -        results.closedWorld.abstractValueDomain.dynamicType;
  +    return results.resultOfMember(element).returnType;
     }
   
     static AbstractValue inferredTypeForMember(
         MemberEntity element, GlobalTypeInferenceResults results) {
  -    return results.resultOfMember(element).type ??
  -        results.closedWorld.abstractValueDomain.dynamicType;
  +    return results.resultOfMember(element).type;
     }
   
     static AbstractValue inferredTypeForParameter(
         Local element, GlobalTypeInferenceResults results) {
  -    return results.resultOfParameter(element) ??
  -        results.closedWorld.abstractValueDomain.dynamicType;
  +    return results.resultOfParameter(element);
     }
   
     static AbstractValue inferredResultTypeForSelector(Selector selector,
         AbstractValue receiver, GlobalTypeInferenceResults results) {
  -    return results.resultTypeOfSelector(selector, receiver) ??
  -        results.closedWorld.abstractValueDomain.dynamicType;
  +    return results.resultTypeOfSelector(selector, receiver);
     }
   
     static AbstractValue fromNativeBehavior(
  
positive.code: // Copyright (c) 2012, 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
  
  import '../common/elements.dart' show CommonElements;
  import '../elements/entities.dart';
  
negative.code:       if (type == SpecialType.JsObject) {
          return abstractValueDomain
              .createNonNullExact(commonElements.objectClass);
        }
        if (type is DartType) {
          if (type is VoidType) {
            return abstractValueDomain.nullType;
          }
          if (closedWorld.dartTypes.isTopType(type)) {
            return abstractValueDomain.dynamicType;
          }
          if (type == commonElements.nullType) {
            return abstractValueDomain.nullType;
          }
          if (type is InterfaceType) {
            return abstractValueDomain.createNonNullSubtype(type.element);
          }
        }
        throw 'Unexpected type $type';
      }
  
      AbstractValue result =
  