code: @Override
    public synchronized ApiFuture<Void> add(RowMutation rowMutation) {
      Preconditions.checkNotNull(rowMutation, "mutation details cannot be null");
      final ApiFuture<Void> response = bulkMutateBatcher.add(rowMutation);
      operationAccountant.registerOperation(ApiFutureUtil.adapt(response));
      return response;
    }
docs: {@inheritDoc}