docs: def get_batch(self, filename=None):
          """Returns a batch instance given the filename.
          """
          try:
              history = self.history_model.objects.get(filename=filename)
          except self.history_model.DoesNotExist as e:
              raise TransactionsFileQueueError(
                  f"Batch history not found for '{filename}'."
              ) from e
          if history.consumed:
              raise TransactionsFileQueueError(
                  f"Batch closed for '{filename}'. Got consumed=True"
              )
          batch = self.batch_cls()
          batch.batch_id = history.batch_id
          batch.filename = history.filename
          return batch