apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/service/ClusterService.java/ClusterService/isClusterNameUnique
class ClusterService:  public boolean isClusterNameUnique(String appId, String clusterName) {
    Objects.requireNonNull(appId, "AppId must not be null");
    Objects.requireNonNull(clusterName, "ClusterName must not be null");
    return Objects.isNull(clusterRepository.findByAppIdAndName(appId, clusterName));
  }