anchor.diff:    @override
     void registerDynamicUse(DynamicUse dynamicUse) {
       _dynamicUses ??= Setlet.of(worldImpact.dynamicUses);
  -    _dynamicUses.add(dynamicUse);
  +    _dynamicUses!.add(dynamicUse);
     }
   
     @override
     void registerTypeUse(TypeUse typeUse) {
       _typeUses ??= Setlet.of(worldImpact.typeUses);
  -    _typeUses.add(typeUse);
  +    _typeUses!.add(typeUse);
     }
   
     @override
  
positive.code: class TransformedWorldImpact extends WorldImpactBuilder {
    final WorldImpact worldImpact;
  
    Setlet<StaticUse> _staticUses;
    Setlet<TypeUse> _typeUses;
    Setlet<DynamicUse> _dynamicUses;
    Setlet<ConstantUse> _constantUses;
  
    TransformedWorldImpact(this.worldImpact);
  
    @override
    MemberEntity get member => worldImpact.member;
  
    @override
    bool get isEmpty {
  
negative.code:   @override
    void registerConstantUse(ConstantUse constantUse) {
      _constantUses ??= Setlet.of(worldImpact.constantUses);
      _constantUses!.add(constantUse);
    }
  
    @override
  