Created Unassigned: Package from NuGet: Less compilation fails with Bootstrap 3 [53]

I intalled the NuGet package for BundleTransformer: LESS today and when I try to make a bundle for bootstrap files, it fails. The code used to make the bundle is the following:

var cssBundle = new Bundle("~/Content/bootstrap") {Builder = new NullBuilder()};
cssBundle.IncludeDirectory("~/Content/bootstrap/", "*.less");
cssBundle.Transforms.Add(new CssTransformer());
bundles.Add(cssBundle);

var jsBundle = new Bundle("~/Script/bootstrap") { Builder = new NullBuilder() };
jsBundle.Include("~/Script/bootstrap/bootstrap.js");
jsBundle.Transforms.Add(new JsTransformer());
bundles.Add(jsBundle);

And I get the next error:

File: /Content/bootstrap/alerts.less
Line number: 10
Column number: 11

Source error:

Line 9: .alert {
Line 10: padding: @alert-padding;
-------------------^

Line 11: margin-bottom: @line-height-computed;

Seems like it not compile well the variables defined in other .less file. Any idea?? I use the last version of Transformer and Bootstrap