code: public static Map<Integer, Long> getSuspensionLevelsBySubsystem(EntityManager em, SubSystem subSystem) {
          return findBySubsystem(em, subSystem).getLevels();
      }
docs: Retrieves the suspension levels for the given subsystem.
  
  @param   em         The EntityManager to use.
  @param   subSystem  The subsystem for which to retrieve suspension levels.
  
  @return  The suspension levels for the given subsystem.