anchor.diff:    /// If the is tests were generated with `storeFunctionTypeInMetadata` set to
     /// `false`, this field is `null`, and the [properties] contain a property
     /// that encodes the function type.
  -  jsAst.Expression functionTypeIndex;
  +  jsAst.Expression? functionTypeIndex;
   
     /// The properties that must be installed on the prototype of the
     /// JS constructor of the [ClassEntity] for which the is checks were
  
positive.code:       if (storeFunctionTypeInMetadata && functionTypeIndex != null) {
          result.functionTypeIndex = functionTypeIndex;
        } else {
          jsAst.Expression encoding =
              generatedCode[classFunctionType.signatureFunction];
          if (classFunctionType.signatureFunction == null) {
            // The signature function isn't live.
            return;
          }
          if (functionTypeIndex != null) {
            if (isDeferred) {
              // The function type index must be offset by the number of types
  
negative.code: 
    void forEachProperty(
        Sorter sorter, void f(jsAst.Name name, jsAst.Node expression)) {
      void handleTypeTest(TypeTest? typeTest) {
        if (typeTest == null) return;
        f(typeTest.name, typeTest.expression);
      }
  
      for (ClassEntity cls in sorter.sortClasses(_properties.keys)) {
        TypeTests typeTests = _properties[cls]!;
        handleTypeTest(typeTests.isTest);
        handleTypeTest(typeTests.substitution);
        handleTypeTest(typeTests.signature);
  