allow empty files

Gruntfile.js

@@ -118,7 +118,7 @@ module.exports = function(grunt) {
       },
       main: {
         // src is used to build list of less files to compile
-        src: ['test/less/*.less', '!test/less/javascript.less', '!test/less/urls.less'],
+        src: ['test/less/*.less', '!test/less/javascript.less', '!test/less/urls.less', '!test/less/empty.less'],
         options: {
           helpers: 'test/browser/runner-main-options.js',
           specs: 'test/browser/runner-main-spec.js',

lib/less/parser.js

@@ -716,7 +716,7 @@ less.Parser = function Parser(env) {
             primary: function () {
                 var mixin = this.mixin, $re = _$re, root = [], node;
 
-                while (true)
+                while (current)
                 {
                     node = this.extendRule() || mixin.definition() || this.rule() || this.ruleset() ||
                         mixin.call() || this.comment() || this.directive();