code: public List<String> writeBulk(final List<String> keys) throws Exception {
          List<String> responses = new ArrayList<>(keys.size());
          for (String key : keys) {
              String response = writeSingle(key);
              responses.add(response);
          }
          return responses;
      }
docs: Perform a bulk write operation
  @return a list of response codes
  @throws Exception