Branch.transitionToInformationType breaks when making a subscriberless branch private

Branch.transitionToInformationType breaks when making a branch private if it has no subscribers:

Module lp.code.model.branch, line 272, in transitionToInformationType
self, self.subscribers)
Module lp.registry.services.sharingservice, line 181, in getPeopleWithoutAccess
return set(people).difference(set(result_set))
Module storm.store, line 997, in __iter__
result = self._store._connection.execute(self._get_select())
Module storm.databases.postgres, line 266, in execute
return Connection.execute(self, statement, params, noresult)
Module storm.database, line 238, in execute
raw_cursor = self.raw_execute(statement, params)
Module storm.databases.postgres, line 276, in raw_execute
return Connection.raw_execute(self, statement, params)
Module storm.database, line 322, in raw_execute
self._check_disconnect(raw_cursor.execute, *args)
Module storm.database, line 371, in _check_disconnect
return function(*args, **kwargs)
ProgrammingError: syntax error at or near ")"<br /> LINE 1: ...essArtifactGrant.artifact = 6)) AND Person.id IN () ORDER BY...<br /> ^<br /> <br />