code: function mergeAdjacentWhitespace(node) {
      var i = node.content.length - 1;
      while (i-- > 0) {
        if (node.get(i).is('space') &&
            node.get(i + 1) && node.get(i + 1).is('space')) {
          node.get(i).content += node.get(i + 1).content;
          node.removeChild(i + 1);
        }
      }
    }
docs: Removing ruleset nodes from tree may result in two adjacent whitespace
  nodes which is not correct AST:
  [space, ruleset, space] => [space, space]
  To ensure correctness of further processing we should merge such nodes
  into one:
  [space, space] => [space]