code: public void setJobGroup (final String jobGroup)
    {
      if (jobGroup != null && jobGroup.trim ().length () == 0)
        throw new IllegalArgumentException ("Group name cannot be null or empty.");
  
      if (jobGroup == null)
        m_sJobGroup = IScheduler.DEFAULT_GROUP;
      else
        m_sJobGroup = jobGroup;
    }
docs: <p>
  Set the name of the associated
  <code>{@link com.helger.quartz.IJobDetail}</code>'s group.
  </p>
  
  @param jobGroup
  if <code>null</code>, Scheduler.DEFAULT_GROUP will be used.
  @exception IllegalArgumentException
  if group is an empty string.