AttributeError at admin: 'NoneType' object has no attribute 'startswith' - django-models

Question

Below is my error:
AttributeError at /admin/r/31/3/
'NoneType' object has no attribute 'startswith'
Request Method: GET
Request URL: http://127.0.0.1:8000/admin/r/31/3/
Django Version: 3.2.13
Exception Type: AttributeError
Exception Value:
'NoneType' object has no attribute 'startswith'
Exception Location: C:\github\project\venv\lib\site-packages\django\contrib\contenttypes\views.py, line 41, in shortcut
Python Executable: C:\github\project\venv\Scripts\python.exe
Python Version: 3.7.1
This occurs when I'm trying to access certain type of model via admin, since I cannot access it through the tag related to get_absolute_url function of the model. The template appears, but never let me access the get_absolute_url.
The thing is, there is another model in another app which is almost identical in views.py, urls.py and models.py but only difference is 'permission_required' decorator which I can't sure if it's outdated.
views.py of error model.
from django.urls import reverse_lazy
from django.shortcuts import render, get_object_or_404
from django.views.generic import ListView, DetailView, CreateView, UpdateView
from django.contrib.auth.mixins import LoginRequiredMixin, UserPassesTestMixin
from django.contrib.auth.decorators import login_required, permission_required
from .models import *
def landing(request):
return render(
request,
'instructor/landing.html'
)
def paymentrequired(request):
return render(
request,
'instructor/paymentrequired.html'
)
def lecture_in_category(request, category_slug=None):
current_category = get_object_or_404(Category, slug=category_slug)
categories = Category.objects.all()
lectures = Lecture.objects.filter(category=current_category)
return render(request, 'instructor/lecture_list.html',
{'current_category': current_category, 'categories': categories, 'lectures': lectures})
class LectureDetail(DetailView):
model = Lecture
def lecture_detail(request, id):
lecture = get_object_or_404(Lecture, id=id)
return render(request, 'instructor/lecture_detail.html', {'lecture':lecture})
# Create your views here.
models.py of the error page
from django.db import models
from django.contrib.auth.models import User
from django.urls import reverse
import os
class Category(models.Model):
name = models.CharField(max_length=200, db_index=True)
meta_description = models.TextField(blank=True)
slug = models.SlugField(max_length=200, db_index=True, unique=True, allow_unicode=True)
class Meta:
ordering = ['name']
verbose_name = 'category'
verbose_name_plural = 'categories'
def __str__(self):
return self.name
def get_absolute_url(self):
return reverse('instructor:lecture_in_category', args=[self.slug])
class Lecture(models.Model):
title = models.CharField(max_length=40)
description = models.CharField(max_length=200, blank=True)
video_key = models.CharField(max_length=20, blank=True)
slug = models.SlugField(max_length=200, db_index=True, unique=True, allow_unicode=True)
video_upload = models.FileField(upload_to='instructor/files/%Y/%m/%d', blank=True)
head_image = models.ImageField(upload_to='instructor/images/%Y/%m/%d', blank=True)
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
available_display = models.BooleanField('Display', default=True)
author = models.CharField(max_length=40)
category = models.ForeignKey(Category, null=True, blank=True, on_delete=models.SET_NULL)
class Meta:
ordering = ['-created_at']
index_together = [['id', 'slug']]
def __str__(self):
return self.title
def get_absolute_url(self):
reverse('instructor:lecture_detail', args=[self.id, self.slug])
# Create your models here.
urls.py of the error page
from django.urls import path
from . import views
from .views import *
app_name = 'instructor'
urlpatterns = [
path('', landing, name='landing'),
path('<slug:category_slug>/', lecture_in_category, name='lecture_list_category'),
path('<int:id>/<lecture_slug>/', LectureDetail.lecture_detail, name="lecture_detail"),
path('payment_required/', paymentrequired, name="paymentrequired"),
]
this is my database setting
DATABASES = {
'default': {
'ENGINE': os.environ.get("SQL_ENGINE", 'django.db.backends.sqlite3'),
'NAME': os.environ.get('SQL_DATABASE', os.path.join(BASE_DIR, 'db.sqlite3')),
'USER': os.environ.get('SQL_USER', 'user'),
'PASSWORD': os.environ.get('SQL_PASSWORD', 'password'),
'HOST': os.environ.get('SQL_HOST', 'localhost'),
'PORT': os.environ.get("SQL_PORT", '5432'),
}
}
This is the traceback.
Traceback (most recent call last):
File "C:\github\rhizomeedu\venv\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
response = get_response(request)
File "C:\github\rhizomeedu\venv\lib\site-packages\django\core\handlers\base.py", line 181, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\github\rhizomeedu\venv\lib\site-packages\django\contrib\admin\sites.py", line 250, in wrapper
return self.admin_view(view, cacheable)(*args, **kwargs)
File "C:\github\rhizomeedu\venv\lib\site-packages\django\utils\decorators.py", line 130, in _wrapped_view
response = view_func(request, *args, **kwargs)
File "C:\github\rhizomeedu\venv\lib\site-packages\django\views\decorators\cache.py", line 44, in _wrapped_view_func
response = view_func(request, *args, **kwargs)
File "C:\github\rhizomeedu\venv\lib\site-packages\django\contrib\admin\sites.py", line 232, in inner
return view(request, *args, **kwargs)
File "C:\github\rhizomeedu\venv\lib\site-packages\django\contrib\contenttypes\views.py", line 41, in shortcut
if absurl.startswith(('http://', 'https://', '//')):
AttributeError: 'NoneType' object has no attribute 'startswith'
With that model, the error doesn't appear so I once deleted the decorator but the result was same.
So I assume it's about settings.py ..?
Help me.