Bad credential not correctly handled

[antonincms]

When I tried to login with an inexistent user / password, I got :

Internal Server Error: /accounts/login/
Traceback (most recent call last):
  File "/srv/langate2000/langate/langate/insalan_auth/insalan_backend.py", line 38, in authenticate
    user = UserModel._default_manager.get_by_natural_key(username)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/contrib/auth/base_user.py", line 44, in get_by_natural_key
    return self.get(**{self.model.USERNAME_FIELD: username})
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/db/models/query.py", line 399, in get
    self.model._meta.object_name
django.contrib.auth.models.User.DoesNotExist: User matching query does not exist.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/core/handlers/base.py", line 126, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/core/handlers/base.py", line 124, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/views/generic/base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/utils/decorators.py", line 45, in _wrapper
    return bound_method(*args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/views/decorators/debug.py", line 76, in sensitive_post_parameters_wrapper
    return view(request, *args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/utils/decorators.py", line 45, in _wrapper
    return bound_method(*args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/utils/decorators.py", line 142, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/utils/decorators.py", line 45, in _wrapper
    return bound_method(*args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/views/decorators/cache.py", line 44, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/contrib/auth/views.py", line 61, in dispatch
    return super().dispatch(request, *args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/views/generic/base.py", line 88, in dispatch
    return handler(request, *args, **kwargs)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/views/generic/edit.py", line 141, in post
    if form.is_valid():
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/forms/forms.py", line 185, in is_valid
    return self.is_bound and not self.errors
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/forms/forms.py", line 180, in errors
    self.full_clean()
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/forms/forms.py", line 382, in full_clean
    self._clean_form()
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/forms/forms.py", line 409, in _clean_form
    cleaned_data = self.clean()
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/contrib/auth/forms.py", line 196, in clean
    self.user_cache = authenticate(self.request, username=username, password=password)
  File "/srv/langate2000/venv/lib/python3.7/site-packages/django/contrib/auth/__init__.py", line 73, in authenticate
    user = backend.authenticate(request, **credentials)
  File "/srv/langate2000/langate/langate/insalan_auth/insalan_backend.py", line 72, in authenticate
    raise BadCredentialsException
langate.insalan_auth.insalan_backend.BadCredentialsException

Could I have validation of this as a bug ?