AttributeError: 'NoneType' object has no attribute 'title' on package differences page

OOPS-82de6bc2588f8b41afd7a2d53e935c8a

 Traceback (most recent call last):
  Module zope.publisher.publish, line 134, in publish
    result = publication.callObject(request, obj)
  Module lazr.restful.publisher, line 211, in callObject
    WebServicePublicationMixin, self).callObject(request, object)
  Module lp.services.webapp.publication, line 499, in callObject
    return mapply(ob, request.getPositionalArguments(), request)
  Module zope.publisher.publish, line 109, in mapply
    return debug_call(obj, args)
   - __traceback_info__: <security proxied lazr.restful._resource.EntryFieldResource instance at 0x16bf69d0>
  Module zope.publisher.publish, line 115, in debug_call
    return obj(*args)
  Module lazr.restful._resource, line 914, in __call__
    result = self.do_GET()
  Module lazr.restful._resource, line 1286, in do_GET
    return self._representation(media_type)
  Module lazr.restful._resource, line 1318, in _representation
    self.context.name, self.context.field, CLOSEUP_DETAIL)
  Module lazr.restful._resource, line 815, in _unmarshallField
    self.entry, value)
  Module lazr.restful.marshallers, line 331, in unmarshall_to_closeup
    if value.title == item.title:
AttributeError: 'NoneType' object has no attribute 'title'