This fixes:

  Traceback (innermost last):
    ...
    Module transaction._transaction, line 393, in _commitResources
      rm.tpc_vote(self)
    Module ZODB.Connection, line 797, in tpc_vote
      s = vote(transaction)
    Module neo.client.Storage, line 95, in tpc_vote
      return self.app.tpc_vote(transaction)
    Module neo.client.app, line 546, in tpc_vote
      self.waitStoreResponses(txn_context)
    Module neo.client.app, line 539, in waitStoreResponses
      _waitAnyTransactionMessage(txn_context)
    Module neo.client.app, line 160, in _waitAnyTransactionMessage
      self._handleConflicts(txn_context)
    Module neo.client.app, line 471, in _handleConflicts
      assert oid is None, (oid, serial)
  AssertionError: ('\x00\x00\x00\x00\x00\x02\n\xe3', '\x03\xca\xad\xcb!\x92\xb6\x9c')