Redirect to login page without losing content of form

I have problem similar to this one: https://stackoverflow.com/questions/50272631/django-form-data-lost-on-making-login-required-on-post

I want answer to be added if user is logged in otherwise redirect user to login page, let him login and then add his answer. My problem is that I lose content of the form.

At the moment I'm getting this errror:

The view questions.views.answer didn't return an HttpResponse object. It returned None instead.

def question(request, question_id):

question = get_object_or_404(Question, pk=question_id)

form = AnswerForm()

return render(request, 'questions/question.html', {'question': question, 'form' : form},)

@login_required

def answer(request, question_id):

question = get_object_or_404(Question, pk=question_id)

form = AnswerForm(request.POST) if request.method == 'POST' else AnswerForm()

if form.is_valid():

answer = form.save(commit=False)

answer.author = request.user

answer.question = question

answer.save()

return HttpResponseRedirect(reverse('question', args=(question.id,)))

<form method="POST" action="{% url 'answer' question.id %}">

{% csrf_token %}

{{form.as_p}}

<input type="submit" value="Odpowiedz">

</form>

form method="post" action="{% url 'login' %}">

{% csrf_token %}

{{ form.as_p }}

<input type="hidden" name="next" value="{{request.GET.next}}" />

<input type="submit" value="login" />

</form>

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