code: public void autoAttachStatsStorageBySessionId(Function<String, StatsStorage> statsStorageProvider) {
          if (statsStorageProvider != null) {
              this.statsStorageLoader = new StatsStorageLoader(statsStorageProvider);
          }
      }
docs: Auto-attach StatsStorage if an unknown session ID is passed as URL path parameter in multi-session mode
  @param statsStorageProvider function that returns a StatsStorage containing the given session ID