public void addHistory(UpgradeHistoryEntity historicalEntry) {
    if (null == upgradeHistory) {
      upgradeHistory = new ArrayList<>();
    }

    upgradeHistory.add(historicalEntry);
  }
Adds a historical entry for a service component in this upgrade.

@param historicalEntry
         the entry to add.
ambari-server/src/main/java/org/apache/ambari/server/orm/entities/UpgradeEntity.java