Django Admin delete user exception - Django Phone number

Question

I have a django project which was working fine. I got the requirement to include phone verification so i used twilio and used the django [phone number][1]. I did the verification part and everything is working fine until i noticed the following exception when i tried to delete a user from admin panel.

I am not 100% sure if it has anything to do with phone number per this is the only new thing added to project. I tried adding and updating new user from admin panel and it worked fine. The issue is in deletion of user.

Request URL: http://127.0.0.1:8000/admin/projectapp/customuser/

Django Version: 3.0.8
Python Version: 3.8.4
Installed Applications:
['django.contrib.admin',
 'django.contrib.gis',
 'projectapp',
 'django.contrib.sites',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'phonenumber_field',
 'verify_email.apps.VerifyEmailConfig',
 'allauth',
 'allauth.account',
 'allauth.socialaccount',
 'allauth.socialaccount.providers.google']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']



Traceback (most recent call last):
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
    response = get_response(request)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\options.py", line 607, in wrapper
    return self.admin_site.admin_view(view)(*args, **kwargs)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\utils\decorators.py", line 130, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\views\decorators\cache.py", line 44, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\sites.py", line 231, in inner
    return view(request, *args, **kwargs)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\utils\decorators.py", line 43, in _wrapper
    return bound_method(*args, **kwargs)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\utils\decorators.py", line 130, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\options.py", line 1704, in changelist_view
    response = self.response_action(request, queryset=cl.get_queryset(request))
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\options.py", line 1390, in response_action
    response = func(self, request, queryset)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\actions.py", line 28, in delete_selected
    deletable_objects, model_count, perms_needed, protected = modeladmin.get_deleted_objects(queryset, request)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\options.py", line 1826, in get_deleted_objects
    return get_deleted_objects(objs, request, self.admin_site)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\utils.py", line 151, in get_deleted_objects
    to_delete = collector.nested(format_callback)
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\utils.py", line 211, in nested
    roots.extend(self._nested(root, seen, format_callback))
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\utils.py", line 195, in _nested
    children.extend(self._nested(child, seen, format_callback))
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\utils.py", line 197, in _nested
    ret = [format_callback(obj)]
  File "D:\installedSoft\Python\Python38-32\lib\site-packages\django\contrib\admin\utils.py", line 126, in format_callback
    no_edit_link = '%s: %s' % (capfirst(opts.verbose_name), obj)

Exception Type: TypeError at /admin/projectapp/customuser/
Exception Value: __str__ returned non-string (type NoneType)

Here is my model class for user

class CustomUser(AbstractUser):
    username = None
    email = models.EmailField(_('email address'), unique=True)
    zipcode = models.CharField(max_length=10, blank=True,verbose_name='zip code')
    full_name = models.CharField(max_length=100, blank=True,verbose_name='Full name')
    gender = models.CharField(max_length=8, blank=True,verbose_name='gender')
    donation_amount = models.FloatField(max_length=10, blank=False,default=0, verbose_name='donation amount' )
    phone_number = PhoneNumberField(null=False, blank=False, unique=True) #models.BigIntegerField(blank=True)
    country_code = models.IntegerField(default=1)
    two_factor_auth = models.BooleanField(default=False)
    is_verified =  models.BooleanField(default=False)

    USERNAME_FIELD = 'email'
    REQUIRED_FIELDS =  ['full_name', 'phone_number', 'country_code']

    objects = CustomUserManager()

    def __str__(self):
        return self.email

Answer 1

Change the str method of your custom user model. Make sure that the method never returns None.