For the nexus 5 bots here: https://chromeperf.appspot.com/group_report?bug_id=919478

'NoneType' object has no attribute 'startswith' (/base/alloc/tmpfs/dynamic_runtimes/python27g/350d926c06a7e859/python27/python27_lib/versions/third_party/webapp2-2.5.2/webapp2.py:1552)
Traceback (most recent call last):
  File "/base/alloc/tmpfs/dynamic_runtimes/python27g/350d926c06a7e859/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/350d926c06a7e859/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/350d926c06a7e859/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/350d926c06a7e859/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/350d926c06a7e859/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/350d926c06a7e859/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~chromeperf/pinpoint:clean-simonhatch-42feef6e.415583852685194307/dashboard/api/api_request_handler.py", line 90, in post
    results = self.Post(*args)
  File "/base/data/home/apps/s~chromeperf/pinpoint:clean-simonhatch-42feef6e.415583852685194307/dashboard/pinpoint/handlers/new.py", line 28, in Post
    job = _CreateJob(self.request)
  File "/base/data/home/apps/s~chromeperf/pinpoint:clean-simonhatch-42feef6e.415583852685194307/dashboard/pinpoint/handlers/new.py", line 44, in _CreateJob
    changes = _ValidateChanges(arguments)
  File "/base/data/home/apps/s~chromeperf/pinpoint:clean-simonhatch-42feef6e.415583852685194307/dashboard/pinpoint/handlers/new.py", line 98, in _ValidateChanges
    'git_hash': arguments.get('start_git_hash'),
  File "/base/data/home/apps/s~chromeperf/pinpoint:clean-simonhatch-42feef6e.415583852685194307/dashboard/pinpoint/models/change/commit.py", line 190, in FromDict
    if repository.startswith('https://'):
AttributeError: 'NoneType' object has no attribute 'startswith'