IndexError: list index out of range
  File "django/core/handlers/base.py", line 149, in get_response
    response = self.process_exception_by_middleware(e, request)
  File "django/core/handlers/base.py", line 147, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "django/views/decorators/csrf.py", line 58, in wrapped_view
    return view_func(*args, **kwargs)
  File "django/views/generic/base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "rest_framework/views.py", line 466, in dispatch
    response = self.handle_exception(exc)
  File "rest_framework/views.py", line 463, in dispatch
    response = handler(request, *args, **kwargs)
  File "rest_framework/generics.py", line 210, in get
    return self.retrieve(request, *args, **kwargs)
  File "activities/views.py", line 414, in retrieve
    points = stats.points()
  File "activities/utils.py", line 499, in monthly
    last_point = points[-1][str(until)]