def parse_revision_spec(self, revisions=[]):
        return {
            'base': None,
            'tip': None,
        }
Constructor for the Schedule class
dataset/ETHPy150Open reviewboard/rbtools/rbtools/clients/__init__.py/SCMClient.parse_revision_spec--crossover with--dataset/ETHPy150Open coursera/dataduct/dataduct/pipeline/schedule.py/Schedule.__init__