Resolving default configuration error

So, when I was trying to build my jekyll site without setting no `sass` configuration in `_config.yml`, I was getting this error:

>C:\wrks\git\kelvinst.github.io
>λ jekyll build
>Configuration file: C:/wrks/git/kelvinst.github.io/_config.yml
>            Source: C:/wrks/git/kelvinst.github.io
>       Destination: C:/wrks/git/kelvinst.github.io/_site
>      Generating... error: undefined method `[]' for nil:NilClass. Use --trace to view backtrace

The error was pretty easy to solve (see the code).
Hope to see this in master soon.

Thanks.