질문 생성시에 내용을 넣지 않으면 그냥 에러화면으로 넘어가 버리네요.

질문 수정시에는 제목이나 내용을 지워보면 워닝이 뜨는데.

같은 폼에서 에러 부분 인클류드 해서 쓰는데 왜 이런 결과가 나올까요?

{% extends 'base.html' %}
{% block content %}
<div class="container">
    <h5 class="my-3 border-bottom pb-2">질문등록</h5>
    <form method="post" class="post-form my-3">
        {% csrf_token %}
        {% include "form_errors.html" %}
        <div class="mb-3">
            <label for="subject" class="form-label">제목</label>
            <input type="text" class="form-control" name="subject" id="subject"
                   value="{{ form.subject.value|default_if_none:'' }}">
        </div>
        <div class="mb-3">
            <label for="content" class="form-label">내용</label>
            <textarea class="form-control" name="content"
                      id="content" rows="10">{{ form.content.value|default_if_none:'' }}</textarea>
        </div>
        <button type="submit" class="btn btn-primary">저장하기</button>
    </form>
</div>
{% endblock %}

from django.contrib import messages
from django.contrib.auth.decorators import login_required
from django.shortcuts import render, get_object_or_404, redirect
from django.utils import timezone

from ..models import Question
from ..forms import QuestionForm


#질문등록

@login_required(login_url='common:login')
def question_create(request):
    if request.method == 'POST':
        form = QuestionForm(request.POST)
        if form.is_valid:
            question = form.save(commit=False)
            question.author = request.user
            question.create_date = timezone.now()
            question.save()
            return redirect('board:index')
    else:
        form = QuestionForm()
    context = {'form': form}
    return render(request, 'board/question_form.html', context)


# 질문수정

@login_required(login_url='common:login')
def question_modify(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    if request.user != question.author:
        messages.error(request, '수정권한이 없습니다.')
        return redirect('board:detail', question_id=question.id)
    if request.method == "POST":
        form = QuestionForm(request.POST, instance=question)
        if form.is_valid():
            question = form.save(commit=False)
            question.author = request.user
            question.modify_date = timezone.now()
            question.save()
            return redirect('board:detail', question_id = question.id)
    else:
        form = QuestionForm(instance=question)
    context = {'form': form}
    return render(request, 'board/question_form.html', context)


# 질문삭제
@login_required(login_url='common:login')
def question_delete(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    if request.user != question.author:
        messages.error(request, '삭제권한이 없습니다.')
        return redirect('board:detail', question_id=question.id)
    question.delete()
    return redirect('board:index')