close, but here `size` is actually `nil`! Since there is no argument called `size` on the grow method, `size` will currently be a local variable created when this method is run, but since we haven't set `size` to anything, it will currently be `nil` and this method will end up erroring out (you can't add 1 to `nil` after all).

The correct answer here would have been `@size = @size + 1`.