def METHOD_NAME(self, request, model_admin):
    users = list(
        set(
            QueuedJob.objects.filter(
                submission__problem_instance__contest=request.contest
            ).values_list('submission__user__id', 'submission__user__username')
        )
    )
    if (None, None) in users:
        users = [x for x in users if x != (None, None)]
        users.append(('None', _("(None)")))
    return users