Internal Server Error

The server has either erred or is incapable of performing the requested operation.

Traceback (most recent call last):
  File "/base/alloc/tmpfs/dynamic_runtimes/python27g/abc1bb91493545df/python27/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 1535, in __call__
    rv = self.handle_exception(request, response, e)
  File "/base/alloc/tmpfs/dynamic_runtimes/python27g/abc1bb91493545df/python27/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 1529, in __call__
    rv = self.router.dispatch(request, response)
  File "/base/alloc/tmpfs/dynamic_runtimes/python27g/abc1bb91493545df/python27/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 1278, in default_dispatcher
    return route.handler_adapter(request, response)
  File "/base/alloc/tmpfs/dynamic_runtimes/python27g/abc1bb91493545df/python27/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 1102, in __call__
    return handler.dispatch()
  File "/base/alloc/tmpfs/dynamic_runtimes/python27g/abc1bb91493545df/python27/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 572, in dispatch
    return self.handle_exception(e, self.app.debug)
  File "/base/alloc/tmpfs/dynamic_runtimes/python27g/abc1bb91493545df/python27/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py", line 570, in dispatch
    return method(*args, **kwargs)
  File "/base/data/home/apps/s~office-trailer-hq/20200420t104243.426113741275049482/main.py", line 139, in get
    nearby_cities = City.query(City.abbreviation == city.abbreviation, City.population >= MIN_POP_SIZE).order(-City.population).fetch(10)
AttributeError: 'NoneType' object has no attribute 'abbreviation'