> Not sure about the explanation on property mapping. While doing debug step by step because i didn't have anymore my json mapped to object i reach the case where server response have a field in JSON "bar", which i didn't use in my Model on my app, and the debug goes to line 150.

Odd, do you have a test case you could put into a gist?

The `error` variable is an argument to the method of type `NSError **`. If the user passes in `NULL`, we wouldn't know where to store the reference to the error object we're creating. Again, this will change anyway.