docs: function round2Index(method, round) {
          if ('undefined' === typeof round) {
              round = this.node.game.getCurrentGameStage().round;
              if (round === 0) {
                  throw new Error('MatcherManager.' + method + ': game stage ' +
                                  'is 0.0.0, please specify a valid round.');
              }
          }
          if ('number' === typeof round) {
              round = this.matcher.normalizeRound(round);
          }
          return round;
      }