crash on NSArray.uniq.map

apologize for bug in previous my pull request.

NSArray.uniq returns NSArray, but it's concrete class is some private class.
And the class does not responds -initWithObjects:count:.

Writing test cases for it is not really possible. Sometimes you get a strange private version of an array type class that is mutable or not mutable and you can't tell.

Specifically what is the crash?