def METHOD_NAME(self, commit = True):
    super(BulletinForm, self).METHOD_NAME(commit = True)
    self.instance.METHOD_NAME()
    previous_tags = self.instance.tags.all()
    tags = self.cleaned_data['tags'].split(",")
    #Excluding unwanted tags
    for prev in previous_tags:
        if not prev.name in tags:
            self.instance.tags.remove(prev)
    for tag in tags:
        tag = tag.strip()
        exist = Tag.objects.filter(name = tag).exists()
        if exist:
            new_tag = Tag.objects.get(name = tag)
        else:
            new_tag = Tag.objects.create(name = tag)
        if not new_tag in self.instance.tags.all():
            self.instance.tags.add(new_tag)
    return self.instance