anchor.diff:  
       List<Object> typesReturned = readTypes();
       List<Object> typesInstantiated = readTypes();
  -    String codeTemplateText = source.readStringOrNull();
  +    String? codeTemplateText = source.readStringOrNull();
       SideEffects sideEffects = SideEffects.readFromDataSource(source);
       int throwBehavior = source.readInt();
       bool isAllocation = source.readBool();
  
positive.code:       return value;
      }
  
      String returns = values['returns'];
      if (returns != null) {
        resolveTypesString(dartTypes, returns, onVar: () {
          typesReturned.add(objectType);
  
negative.code:       TypeLookup lookupType,
        DiagnosticReporter reporter,
        CommonElements commonElements,
        {List<String>? validTags}) {
      void setSideEffects(SideEffects newEffects) {
        behavior.sideEffects.setTo(newEffects);
      }
  