@Override
        public CompletableFuture<ClickHouseResponse> execute(ClickHouseRequest<?> request) {
            CompletableFuture<ClickHouseResponse> future = new CompletableFuture<>();
            future.completeExceptionally(new ConnectException("No client available"));
            return future;
        }
Dummy client which is only used by {@link Agent}.
clickhouse-client/src/main/java/com/clickhouse/client/ClickHouseClientBuilder.java