apollo-common/src/main/java/com/ctrip/framework/apollo/common/http/MultiResponseEntity.java/MultiResponseEntity/addResponseEntity
class MultiResponseEntity:  public void addResponseEntity(RichResponseEntity<T> responseEntity) {
    if (responseEntity == null){
      throw new IllegalArgumentException("sub response entity can not be null");
    }
    entities.add(responseEntity);

  }