code: async def create_checkpoint_if_not_exists_async(self, partition_id):
          
          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
docs: 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