Module zope.tal.talinterpreter, line 271, in __call__
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 531, in do_optTag_tal
  Module zope.tal.talinterpreter, line 513, in no_tag
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 531, in do_optTag_tal
  Module zope.tal.talinterpreter, line 513, in no_tag
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 533, in do_optTag_tal
  Module zope.tal.talinterpreter, line 518, in do_optTag
  Module zope.tal.talinterpreter, line 513, in no_tag
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 852, in do_condition
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 533, in do_optTag_tal
  Module zope.tal.talinterpreter, line 518, in do_optTag
  Module zope.tal.talinterpreter, line 513, in no_tag
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 583, in do_setLocal_tal
  Module zope.tales.tales, line 696, in evaluate
   - URL: /vagrant/buildout/src/plone.app.event/plone/app/event/browser/event_summary.pt
   - Line 28, Column 6
   - Expression: <PythonExpr (data.start.tzinfo.utcoffset(data.start))>
   - Names:
      {'args': (),
       'container': <Container at /Plone/the-event/pre-event-talk>,
       'context': <Container at /Plone/the-event/pre-event-talk>,
       'default': <object object at 0xb74f66c8>,
       'here': <Container at /Plone/the-event/pre-event-talk>,
       'loop': {},
       'nothing': None,
       'options': {},
       'repeat': <Products.PageTemplates.Expressions.SafeMapping object at 0xb1e7ac34>,
       'request': <HTTPRequest, URL=http://localhost:8080/Plone/the-event/pre-event-talk/talkview>,
       'root': <Application at >,
       'template': <Products.Five.browser.pagetemplatefile.ViewPageTemplateFile object at 0xb1e64fec>,
       'traverse_subpath': [],
       'user': <PropertiedUser 'admin'>,
       'view': <Products.Five.metaclass.SimpleViewClass from /vagrant/buildout/src/plone.app.event/plone/app/event/browser/event_summary.pt object at 0xb1e41f2c>,
       'views': <Products.Five.browser.pagetemplatefile.ViewMapper object at 0xb1e5c48c>}
  Module zope.tales.pythonexpr, line 59, in __call__
   - __traceback_info__: (data.start.tzinfo.utcoffset(data.start))
  Module <string>, line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'tzinfo'