Let's say that I have an object reference as follows in coffeescript: 

```
object.param.foo.bar

```

and I want to validate that bar exists? How do I do that?

I believe that `object.param.foo?.bar` tests for the existence of `foo`, returning `undefined` if it does not exist, but that `object.param.foo.bar?` converts the entire expression into a boolean test. 

What I want is something that returns `object.param.foo.bar` if it exists and `undefined` if it does not.