apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/service/NamespaceService.java/NamespaceService/namespaceHasInstances
class NamespaceService:  public boolean namespaceHasInstances(String appId, Env env, String clusterName,
      String namespaceName) {
    return instanceService.getInstanceCountByNamespace(appId, env, clusterName, namespaceName) > 0;
  }