apollo-client/src/main/java/com/ctrip/framework/apollo/internals/PropertiesCompatibleFileConfigRepository.java/PropertiesCompatibleFileConfigRepository/sync
class PropertiesCompatibleFileConfigRepository:  @Override
  protected synchronized void sync() {
    Properties current = configFile.asProperties();

    Preconditions.checkState(current != null, "PropertiesCompatibleConfigFile.asProperties should never return null");

    if (cachedProperties != current) {
      cachedProperties = current;
      this.fireRepositoryChange(configFile.getNamespace(), cachedProperties);
    }
  }