code: def loadRootJob(self):
          
          try:
              with self.readSharedFileStream(self.rootJobStoreIDFileName) as f:
                  rootJobStoreID = f.read().decode('utf-8')
          except NoSuchFileException:
              raise JobException('No job has been set as the root in this job store')
          if not self.exists(rootJobStoreID):
              raise JobException("The root job '%s' doesn't exist. Either the Toil workflow "
                                 "is finished or has never been started" % rootJobStoreID)
          return self.load(rootJobStoreID)
docs: Loads the root job in the current job store.
  
          :raises toil.job.JobException: If no root job is set or if the root job doesn't exist in
                  this job store
          :return: The root job.
          :rtype: toil.jobGraph.JobGraph