code: @Override
    public byte[] toBytes(JobKey jobKey) {
      if (jobKey == null) {
        return Constants.EMPTY_BYTES;
      } else {
        return ByteUtil.join(Constants.SEP_BYTES,
            Bytes.toBytes(jobKey.getCluster()),
            Bytes.toBytes(jobKey.getUserName()),
            Bytes.toBytes(jobKey.getAppId()),
            Bytes.toBytes(jobKey.getEncodedRunId()),
            idConv.toBytes(jobKey.getJobId()));
      }
    }
docs: Returns the byte encoded representation of a JobKey
  
  @param jobKey the JobKey to serialize
  @return the byte encoded representation of the JobKey