serby/save — pull request #6 by domharrington (2012-12-24 14:06:50+00:00)
Title: Ensure falsy ids don't count as being a defined id in memory engine.

Currently in the memory engine any falsy value (apart from `undefined`) that gets passed to create gets set as the `_id` value.

The fix just checks if the value is falsy as opposed to checking `undefined`.