docs: def _delete(self, tx_id):
          """Delete a transaction. Read documentation about CRAB model in https://blog.bigchaindb.com/crab-create-retrieve-append-burn-b9f6d111f460.
  
          :param tx_id: transaction id
          :return:
          """
          txs = self.driver.instance.transactions.get(asset_id=self.get_asset_id(tx_id))
          unspent = txs[-1]
          output_index = 0
          output = unspent['outputs'][output_index]
  
          transfer_input = {
              'fulfillment': output['condition']['details'],
              'fulfills': {
                  'output_index': output_index,
                  'transaction_id': unspent['id']
              },
              'owners_before': output['public_keys']
          }
  
          prepared_transfer_tx = self.driver.instance.transactions.prepare(
              operation='TRANSFER',
              asset=unspent['asset'] if 'id' in unspent['asset'] else {'id': unspent['id']},
              inputs=transfer_input,
              recipients=self.BURN_ADDRESS,
              metadata={
                  'namespace': 'burned',
  
              }
          )
          signed_tx = self.driver.instance.transactions.fulfill(
              prepared_transfer_tx,
              private_keys=self.user.private_key,
          )
          self.driver.instance.transactions.send_commit(signed_tx)