anchor.diff:        if (member.name == Identifiers.call) return;
         // All methods on [Object] are shadowed by [Interceptor].
         if (cls == _commonElements.objectClass) return;
  -      Set<MemberEntity> set = _interceptedElements[member.name] ??= {};
  +      final set = _interceptedElements[member.name!] ??= {};
         set.add(member);
       });
   
  
positive.code:   }
  
    @override
    bool isInterceptedClass(ClassEntity element) {
      if (element == null) return false;
      if (_nativeData.isNativeOrExtendsNative(element)) return true;
      if (interceptedClasses.contains(element)) return true;
  
negative.code:     });
    }
  
    Set<ClassEntity>? nativeSubclassesOfMixin(
        ClassEntity mixin, JClosedWorld closedWorld) {
      Iterable<ClassEntity> uses = closedWorld.mixinUsesOf(mixin);
      Set<ClassEntity>? result;
      for (ClassEntity use in uses) {
        closedWorld.classHierarchy.forEachStrictSubclassOf(use,
            (ClassEntity subclass) {
          if (_nativeData.isNativeOrExtendsNative(subclass)) {
            (result ??= {}).add(subclass);
          }
          return IterationStep.CONTINUE;
        });
  