[BUG] MVC UseResultHandler does not handle nil

```go
app.ConfigureContainer().UseResultHandler(func(next iris.ResultHandler) iris.ResultHandler {
return func(ctx iris.Context, v interface{}) error {
/* this function not being called */
fmt.Println(v)
return next(ctx, v)
}
})

func (c *CustomController) Get() any {
return nil
}
```
I want it to run even if the return value is nil.