TypeError: cannot create weak reference to 'unicode' object

[Jeroen T. Vermeulen]

We're getting tracebacks like this one:

  TypeError: cannot create weak reference to 'unicode' object

    Traceback (most recent call last):
  Module zope.publisher.publish, line 134, in publish
  Module lazr.restful.publisher, line 171, in callObject
  Module canonical.launchpad.webapp.publication, line 428, in callObject
    return mapply(ob, request.getPositionalArguments(), request)
  Module zope.publisher.publish, line 109, in mapply
   - __traceback_info__: <security proxied lazr.restful._resource.CollectionResource instance at 0x2aaac4207250>
  Module zope.publisher.publish, line 115, in debug_call
  Module lazr.restful._resource, line 852, in __call__
  Module lazr.restful._resource, line 1543, in do_GET
  Module lazr.restful._resource, line 1555, in batch
  Module lazr.restful._resource, line 646, in batch
  Module zope.security.management, line 143, in checkPermission
  Module canonical.database.sqlbase, line 726, in block_implicit_flushes_decorator
    return func(*args, **kwargs)
  Module canonical.launchpad.webapp.authorization, line 158, in checkPermission
    cache = wd.setdefault(objecttoauthorize, {})
  Module weakref, line 345, in setdefault
    return self.data.setdefault(ref(key, self._remove),default)
TypeError: cannot create weak reference to 'unicode' object

OOPS-1593A2410, OOPS-1593F916