Generated by SassMeister.com.

SassMeister-input-HTML.html

<div data-am-module="">
  data-am-module=""
</div>

<div data-am-module="blue">
  data-am-module="blue"
</div>

<div data-am-module="large">
  data-am-module="large"
</div>

<div data-am-module="large blue">
  data-am-module="large blue"
</div>

SassMeister-input.scss

// ----
// Sass (v3.4.3)
// Compass (v1.0.1)
// ----

@mixin am($module, $trait: null) {
  @if $trait != null {
    [data-am-#{$module}~="#{$trait}"]{
      @content;
    }
  }
  @else {
    [data-am-#{$module}]{
      @content;
    }
  }
}

@include am(module) {
  color: red;
}

@include am(module, blue) {
  color: blue;
}

@include am(module, large) {
  font-size: 2em;
}

SassMeister-output.css

[data-am-module] {
  color: red;
}

[data-am-module~="blue"] {
  color: blue;
}

[data-am-module~="large"] {
  font-size: 2em;
}

SassMeister-rendered.html

<div data-am-module="">
  data-am-module=""
</div>

<div data-am-module="blue">
  data-am-module="blue"
</div>

<div data-am-module="large">
  data-am-module="large"
</div>

<div data-am-module="large blue">
  data-am-module="large blue"
</div>