IN ADMIN PANEL __str__ returned non-string (type NoneType)

Question

im new to django tryna build up ecommerce project for education purposes. i got this error " str returned non-string (type NoneType)" from admin panel, when try view/change order or orderItem. I try to return str(self)I cant find error, pls guys help me fix it. I almost google all, but i dont understand how to can be type error if i return str(). Pls guys help my find they way to fix it

from django.core.validators import RegexValidator
from django.db import models
from authentication.models import Customer
from catalog.models import Product


# Create your models here.


class Order(models.Model):
    customer = models.ForeignKey(Customer, on_delete=models.SET_NULL, null=True)
    date_order = models.DateTimeField(auto_now_add=True)
    complete = models.BooleanField(default=False, null=True, blank=True)
    transaction_id = models.CharField(max_length=200, null=True, blank=True)

    def __str__(self):
        return str(self.transaction_id)

    @property
    def shipping(self):
        shipping = False
        orderitems = self.orderitem_set.all()
        for i in orderitems:
            if i.product.digital == False:
                shipping = True
        return shipping

    @property
    def get_cart_total(self):
        orderitems = self.orderitem_set.all()
        total = sum([item.get_total for item in orderitems])
        return total

    @property
    def get_cart_items(self):
        orderitems = self.orderitem_set.all()
        total = sum([item.quantity for item in orderitems])
        return total

    class OrderItem(models.Model):
        product = models.ForeignKey(Product, on_delete=models.SET_NULL, null=True)
        order = models.ForeignKey(Order, on_delete=models.SET_NULL, null=True)
        quantity = models.IntegerField(default=0, null=True, blank=True)
        date_added = models.DateTimeField(auto_now_add=True)

    @property
    def get_total(self):
        total = self.product.price * self.quantity
        return total


    class ShippingAddress(models.Model):
         customer = models.ForeignKey(Customer, on_delete=models.SET_NULL, null=True, 
         blank=True)
         order = models.ForeignKey(Order, on_delete=models.SET_NULL, null=True, 
         blank=True)
         phone_regex = RegexValidator(
             regex=r'^(05)\d{9}$'
          )
         mobile = models.CharField(validators=[phone_regex], max_length=60,
                              null=True, blank=True)
         state = models.CharField('Область', max_length=200, null=True)
         city = models.CharField('Город', max_length=200, null=True)
         address = models.CharField('Адрес', max_length=200, null=True, blank=True)
         zipcode = models.CharField('Почтовый индекс', max_length=200, null=True)
         date_added = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.address


    class Wishlist(models.Model):
         customer = models.ForeignKey(Customer, on_delete=models.SET_NULL, null=True, 
         blank=True)
         date_order = models.DateTimeField(auto_now_add=True)
         complete = models.BooleanField(default=False, null=True, blank=True)
         transaction_id = models.CharField(max_length=200, null=True)

    def __str__(self):
        return str(self.id)


    class WishlistItem(models.Model):
         product = models.ForeignKey(Product, on_delete=models.SET_NULL, null=True)
         wishlist = models.ForeignKey(Wishlist, on_delete=models.SET_NULL, null=True)
         quantity = models.IntegerField(default=0, null=True, blank=True)
         date_added = models.DateTimeField(auto_now_add=True)


    def __str__(self):
         return str(self.id)


Here is my views:

    from django.shortcuts import render
    from .models import *
    from django.http import JsonResponse
    import json
    import datetime
    from utils import cookieCart, cartData, guestOrder
    from django.conf import settings
    from django.core.mail import send_mail

   # Create your views here.

    def cart(request):
        data = cartData(request)

        cartItems = data['cartItems']
        order = data['order']
        items = data['items']

         context = {'order': order, 'cartItems': cartItems, 'items': items}
    return render(request, 'main/cart.html', context)


    def checkout(request):
        data = cartData(request)

        cartItems = data['cartItems']
        order = data['order']
        items = data['items']

        context = {'items': items, 'order': order, 'cartItems': cartItems}
    return render(request, 'main/checkout.html', context)


    def wishlist(request):
        data = cartData(request)

        cartItems = data['cartItems']
        customer = request.user.customer
        wishlist, created = Wishlist.objects.get_or_create(customer=customer, 
        complete=False)
        items = wishlist.wishlistitem_set.all()

        context = {
        'items': items,
        'cartItems': cartItems,
        }

    return render(request, 'main/wishlist.html', context)


    def updateItem(request):
        data = json.loads(request.body)
         productId = data['productId']
         action = data['action']
         print('Action:', action)
         print('Product:', productId)

        customer = request.user.customer
        product = Product.objects.get(id=productId)
        order, created = Order.objects.get_or_create(customer=customer, complete=False)

        orderItem, created = OrderItem.objects.get_or_create(order=order, 
    product=product)

    if action == 'add':
        orderItem.quantity = (orderItem.quantity + 1)
    elif action == 'remove':
        orderItem.quantity = (orderItem.quantity - 1)

    orderItem.save()

    if orderItem.quantity <= 0:
        orderItem.delete()

    return JsonResponse('Item was added', safe=False)


    def processOrder(request):
         transaction_id = datetime.datetime.now().timestamp()
          data = json.loads(request.body)

         if request.user.is_authenticated:
            customer = request.user.customer
            order, created = Order.objects.get_or_create(customer=customer, 
         complete=False)
         else:
            customer, order = guestOrder(request, data)

         total = data['form']['total']
         order.transaction_id = transaction_id

    if total == order.get_cart_total:
        order.complete = True
    order.save()

    if order.shipping:
        ShippingAddress.objects.create(
            customer=customer,
            order=order,
            mobile=data['shipping']['mobile'],
            state=data['shipping']['state'],
            city=data['shipping']['city'],
            address=data['shipping']['address'],
            zipcode=data['shipping']['zipcode'],
        )
     print('Data:', request.body)
     return JsonResponse('Payment submitted..', safe=False)

Answer 1

I think culprit is your ShippingAddress __str__ method. It returns address which can be None since it has flag null=True

def __str__(self):
    return self.address # <= can return None

Replace it with f-string (I recommend replacing all str())

def __str__(self):
    return f"{self.address}"

or give some default_name

def __str__(self):
    return self.address or "Default no name string"

Answer 2

Solved problem, the error was in Customer model which is relate to Order model and other. Just replace def str with Bartosz Stasiak advice

def __str__(self):
return f"{self.address}"

It helps to me, thank you so much!