AttributeError: 'NoneType' object has no attribute 'realm'

[Ryan J Ollos]

Found in the logs:

[pid 1149 140573412062976] 2016-01-29 13:06:22,995 Trac[main] ERROR: Internal Server Error: <RequestWithSession "GET '/attachment/attachment/ticket/6109'">, referrer None
Traceback (most recent call last):
  File "/usr/local/virtualenv/1.1dev/lib/python2.7/site-packages/trac/web/main.py", line 607, in _dispatch_request
    dispatcher.dispatch(req)
  File "/usr/local/virtualenv/1.1dev/lib/python2.7/site-packages/trac/web/main.py", line 256, in dispatch
    resp = chosen_handler.process_request(req)
  File "/usr/local/virtualenv/1.1dev/lib/python2.7/site-packages/trac/attachment.py", line 195, in process_request
    if not resource_exists(self.env, parent):
  File "/usr/local/virtualenv/1.1dev/lib/python2.7/site-packages/trac/resource.py", line 468, in resource_exists
    return manager.resource_exists(resource)
  File "/usr/local/virtualenv/1.1dev/lib/python2.7/site-packages/trac/attachment.py", line 380, in resource_exists
    attachment = Attachment(self.env, resource)
  File "/usr/local/virtualenv/1.1dev/lib/python2.7/site-packages/trac/attachment.py", line 661, in __init__
    self.parent_realm = resource.parent.realm
AttributeError: 'NoneType' object has no attribute 'realm'