Normalizer fails when selector.val is undefined

[amansx]

Line 247: normalizer.js

   // normalize interpolated selectors with comma
  group.nodes.forEach(function(selector, i){
    if (!~selector.val.indexOf(',')) return;
    if (~selector.val.indexOf('\\,')) {
      selector.val = selector.val.replace(/\\,/g, ',');
      return;
    }

[iChenLei]

PR welcome, folks.