maccman/sourcemap — pull request #4 by josh (2013-08-20 23:46:31+00:00)
Title: Add failing test for additive identity

`x + 0 = x` and `0 + x = x`, so should hold true when adding an empty mapping.

Consider this real world use case.

``` ruby
mappings.inject(Map.new) { |m, t| t + m }
```

I could use some help fixing this @maccman.