@Override
  public void close() {
    if (rpcClient != null) {
      rpcClient.close();
    }
  }
A class for creating {@link RpcClient} and related stubs used by
{@link AbstractRpcBasedConnectionRegistry}. We need to connect to bootstrap nodes to get the
cluster id first, before creating the final {@link RpcClient} and related stubs.
<p>
See HBASE-25051 for more details.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionRegistryRpcStubHolder.java