apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/entity/Instance.java/Instance/toString
class Instance:  @Override
  public String toString() {
    return MoreObjects.toStringHelper(this)
        .omitNullValues()
        .add("id", id)
        .add("appId", appId)
        .add("clusterName", clusterName)
        .add("dataCenter", dataCenter)
        .add("ip", ip)
        .add("dataChangeCreatedTime", dataChangeCreatedTime)
        .add("dataChangeLastModifiedTime", dataChangeLastModifiedTime)
        .toString();
  }