code: function(index, follow) {
              if (_.isNull(follow)) follow = index;
              var value = "";
              value = index ? "index" : "noindex";
              value =  value + "," + (follow ? "follow" : "nofollow");
              this.meta("robots", value);
              return this;
          }
docs: Active or desactive page indexation using robots meta tag
  
  @method setCrawling
  @param {boolean} index
  @return {boolean} follow