def METHOD_NAME(self):
    name = self.cleaned_data.get('name', '')
    topics = self.subject.topic_subject.all()
    for topic in topics:
        if self.instance.id:
            same_name = topic.resource_topic.filter(name__unaccent__iexact = name).exclude(id = self.instance.id).count()
        else:
            same_name = topic.resource_topic.filter(name__unaccent__iexact = name).count()
        if same_name > 0:
            self._errors['name'] = [_('This subject already has a bulletin with this name')]
            return ValueError
    return name