anchor.diff:              .toSet(),
           node.namedParameters.map((n) => visitType(n.type)).toList(),
           typeVariables ?? const <FunctionTypeVariable>[]);
  -    DartType type = _convertNullability(functionType, node.nullability);
  +    DartType type = _convertNullability(functionType, node);
       for (ir.TypeParameter typeParameter in node.typeParameters) {
         currentFunctionTypeParameters.remove(typeParameter);
       }
  
positive.code:     }
      return _convertNullability(
          _dartTypes.typeVariableType(elementMap.getTypeVariable(node.parameter)),
          node.nullability);
    }
  
    @override
  
negative.code:   DartType visitInterfaceType(ir.InterfaceType node) {
      ClassEntity cls = elementMap.getClass(node.classNode);
      return _convertNullability(
          _dartTypes.interfaceType(cls, visitTypes(node.typeArguments)), node);
    }
  
    @override
    DartType visitFutureOrType(ir.FutureOrType node) {
      return _convertNullability(
          _dartTypes.futureOrType(visitType(node.typeArgument)), node);
    }
  
    @override
  