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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def loadRootJob(self):
 """ 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 """

        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)