apollo-client/src/main/java/com/ctrip/framework/apollo/internals/PropertiesCompatibleFileConfigRepository.java/PropertiesCompatibleFileConfigRepository/setUpstreamRepository
class PropertiesCompatibleFileConfigRepository:  @Override
  public void setUpstreamRepository(ConfigRepository upstreamConfigRepository) {
    //config file is the upstream, so no need to set up extra upstream
  }