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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:
 async def get_checkpoint_async(self, partition_id):
 """ Get the checkpoint data associated with the given partition. Could return null if no checkpoint has been created for that partition. :param partition_id: The partition ID. :type partition_id: str :return: Given partition checkpoint info, or `None` if none has been previously stored. :rtype: ~azure.eventprocessorhost.checkpoint.Checkpoint """

        lease = await self.get_lease_async(partition_id)
        checkpoint = None
        if lease:
            if lease.offset:
                checkpoint = Checkpoint(partition_id, lease.offset,
                                        lease.sequence_number)
        return checkpoint