AttributeError: 'GpxModel' object has no attribute 'calculate_values'

[jedie]

  File "/home/yunohost.app/django-for-runners/venv/lib/python3.9/site-packages/django/views/generic/base.py", line 143, in dispatch
    return handler(request, *args, **kwargs)
  File "/home/yunohost.app/django-for-runners/venv/lib/python3.9/site-packages/for_runners/admin/gpx.py", line 267, in get
    instance.calculate_values()

Exception Type: AttributeError at /django-for-runners/for_runners/gpxmodel/1/calculate_values/
Exception Value: 'GpxModel' object has no attribute 'calculate_values'