import of module Missing._Missing failed

[icemac]

I am using a ZODB created with Zope 2.13 and updated it to use Zope 4. When creating a new object I get:

...
Module ZPublisher.WSGIPublisher, line 239, in publish_module
    request, response, module_info, _publish=_publish)
  Module ZPublisher.WSGIPublisher, line 212, in _publish_response
    reraise(exc.__class__, exc, sys.exc_info()[2])
  Module ZPublisher.WSGIPublisher, line 173, in _publish_response
    response = _publish(request, module_info)
  Module contextlib, line 24, in __exit__
    self.gen.next()
  Module ZPublisher.WSGIPublisher, line 116, in transaction_pubevents
    tm.commit()
  Module transaction._manager, line 131, in commit
    return self.get().commit()
  Module transaction._transaction, line 310, in commit
    reraise(t, v, tb)
  Module transaction._transaction, line 301, in commit
    self._commitResources()
  Module transaction._transaction, line 446, in _commitResources
    reraise(t, v, tb)
  Module transaction._transaction, line 420, in _commitResources
    rm.commit(self)
  Module ZODB.Connection, line 498, in commit
    self._commit(transaction)
  Module ZODB.Connection, line 547, in _commit
    self._store_objects(ObjectWriter(obj), transaction)
  Module ZODB.Connection, line 579, in _store_objects
    p = writer.serialize(obj)  # This calls __getstate__ of obj
  Module ZODB.serialize, line 419, in serialize
    return self._dump(meta, obj.__getstate__())
  Module ZODB.serialize, line 428, in _dump
    self._p.dump(state)
_pickle.PicklingError: Can't pickle <class 'Missing._Missing.V'>: import of module Missing._Missing failed