Returns a batch instance after exporting a batch of txs.

def export_batch(self):
        """Returns a batch instance after exporting a batch of txs.
        """
        batch = self.batch_cls(
            model=self.model, history_model=self.history_model, using=self.using
        )
        if batch.items:
            try:
                json_file = self.json_file_cls(batch=batch, path=self.path)
                json_file.write()
            except JSONDumpFileError as e:
                raise TransactionExporterError(e)
            batch.close()
            return batch
        return None