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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 load_job_from_ref(self):
 """ Loads the job.json into self.job """

        if not self.job_id:
            raise Exception('Job not loaded yet. Use load(id) first.')

        if not os.path.exists(self.git.work_tree + '/aetros/job.json'):
            raise Exception('Could not load aetros/job.json from git repository. Make sure you have created the job correctly.')

        with open(self.git.work_tree + '/aetros/job.json') as f:
            self.job = simplejson.loads(f.read(), object_pairs_hook=collections.OrderedDict)

        if not self.job:
            raise Exception('Could not parse aetros/job.json from git repository. Make sure you have created the job correctly.')

        self.logger.debug('job: ' + str(self.job))