nex3/sass — pull request #361 by petebrowne (2012-04-21 18:50:10+00:00)
Title: Add `nil` literal

Here's a common use use case for a `nil` literal:

``` scss
@mixin block-colors($background-color, $border-color: nil) {
$border-color: darken($background-color, 10%) !default;

background-color: $background-color;
border-color: $border-color;
}
```

This is semantically different than using `false` in conjunction with an `@if` directive. Plus, guarded assignment can be used to set a dynamic default value.