nth() doesn't handle maps

[xzyfer]

This can return the nth pair in a map as well. - http://sass-lang.com/documentation/Sass/Script/Functions.html#nth-instance_method

$map: (foo: bar, bar: baz);

foo {
  a: nth($map, 2);
}

Expected output

foo {
  a: bar baz;
}

Actual output

stdin:4: index out of bounds for `nth($list, $n)`

[esr360]

I still seem to be getting this issue, or at least an issue very similar to this, when using Libsass (I don't get the error when using Ruby Sass):

>> Error: index out of bounds for `nth($list, $n)`
>>         on line 21 of ../../Synergy/src/scss/mixins/_component.scss
>> >>     $namespace: nth(module-tree(&), length(module-tree(&)));

For reference here is the culpable line of code: https://github.com/esr360/Synergy/blob/4715c9ceec3ca1ad664ef0b7a093743b9929e3de/src/scss/mixins/_component.scss#L21

It should be noted that if I change this line:

$namespace: nth(module-tree(&), length(module-tree(&)));

Into this:

$this: module-tree(&);

$namespace: nth($this, length($this));

then it compiles without an error.