ember-cli-csssplit addon usage

ember-cli : 1.13.6 ember : 1.13.5

On ember serve , it fails with "Path or pattern "*.css" did not match any files". I am able to make it work by adding a if check in the addons index.js as

if(type == 'css'){
    var styles = pickFiles(tree, {
        srcDir: '/assets',
        files: files,
        destDir: '/assets'
    });

    return mergeTrees([tree, csss(styles, this.options)], { overwrite: true });
}else{
    return tree;
}

Is this a bug or have i configured somewhere wrongly?