Create the given partition checkpoint if it doesn't exist.Do nothing if it does exist.
        The offset/sequenceNumber for a freshly-created checkpoint should be set to StartOfStream/0.

        :param partition_id: The partition ID.
        :type partition_id: str
        :return: The checkpoint for the given partition, whether newly created or already existing.
        :rtype: ~azure.eventprocessorhost.checkpoint.Checkpoint

async def create_checkpoint_if_not_exists_async(self, partition_id):
        """
        Create the given partition checkpoint if it doesn't exist.Do nothing if it does exist.
        The offset/sequenceNumber for a freshly-created checkpoint should be set to StartOfStream/0.

        :param partition_id: The partition ID.
        :type partition_id: str
        :return: The checkpoint for the given partition, whether newly created or already existing.
        :rtype: ~azure.eventprocessorhost.checkpoint.Checkpoint
        """
        checkpoint = await self.get_checkpoint_async(partition_id)
        if not checkpoint:
            await self.create_lease_if_not_exists_async(partition_id)
            checkpoint = Checkpoint(partition_id)
        return checkpoint