code: public ResourceAssignmentWorkgroupFields addWorkgroupAssignment() throws MPXJException
     {
        if (m_workgroup != null)
        {
           throw new MPXJException(MPXJException.MAXIMUM_RECORDS);
        }
  
        m_workgroup = new ResourceAssignmentWorkgroupFields();
  
        return (m_workgroup);
     }
docs: This method allows a resource assignment workgroup fields record
  to be added to the current resource assignment. A maximum of
  one of these records can be added to a resource assignment record.
  
  @return ResourceAssignmentWorkgroupFields object
  @throws MPXJException if MSP defined limit of 1 is exceeded