我不知道为什么实例不能以 django 的形式工作

Question

views.py：

@login_required
def put(request, id):
    question = get_object_or_404(Question, id=id)
    poll_form = PollForm(request.POST, instance=question)
    print(poll_form)
    choice_forms = [ChoiceForm(request.POST, prefix=str(
        choice.id), instance=choice) for choice in question.choice_set.all()]
    if poll_form.is_valid() and all([cf.is_valid() for cf in choice_forms]):
        new_poll = poll_form.save(commit=False)
        new_poll.created_by = request.user
        new_poll.save()
        for cf in choice_forms:
            new_choice = cf.save(commit=False)
            new_choice.question = new_poll
            new_choice.save()
        return redirect('poll:index')
    context = {'poll_form': poll_form, 'choice_forms': choice_forms}
    return render(request, 'polls/edit_poll.html', context)

edit_poll.html：

{{poll_form.as_table}}

{% for form in choice_forms %}
     {{form.as_table}}
{% endfor %}

models.py：

class Question(models.Model):
    title = models.TextField(null=True, blank=True)
    created_by = models.ForeignKey(User, null=True, blank=True, 
                          related_name="created", on_delete=models.CASCADE)

forms.py：

class PollForm(forms.ModelForm):
    title = forms.CharField(max_length=333, label='Question')

    class Meta:
        model = Question
        fields = ['title']

class ChoiceForm(forms.ModelForm):
    text = forms.CharField(max_length=255, label='Choice')

    class Meta:
        model = Choice
        exclude = ('question',)

当我检查元素时：

<td><ul class="errorlist"><li>This field is required.</li></ul><input 
  type="text" name="title" maxlength="333" required="" id="id_title"></td>

字段是 empty（但它应该由现有的 id 问题和选择填充）但我看到 errorlist 类我不知道。

请帮帮我。

但是当我填写edit表格并尝试update事情时它工作