Interface administration Django

TypeError at /admin/libraryapp/usermanager/add/
cannot unpack non-iterable NoneType object

from django.contrib import admin
from django.contrib.auth.admin import UserAdmin
from django.forms import Textarea
from django.db import models

# Register your models here.
from .models import UserManager


class UserAdminConfig(UserAdmin):
    model = UserManager
    search_fields = ('email', 'user_name')
    list_filter = ('email', 'user_name', 'is_staff', 'is_admin', 'is_active')
    ordering = ('registration_date',)
    list_display = ('email', 'user_name', 'is_staff', 'is_admin', 'is_active')
    fieldsets = (
        (None, {'fields': ('email', 'user_name')}),
        ('Permissions', {'fields': ('is_staff', 'is_admin', 'is_active')}),
    )

    formfield_overrides = {
        models.TextField: {'widget': Textarea(attrs={'rows': 20, 'cols': 20})},
    }

    add_fieldsets = (
        (None, {
            'classes': ('widget',),
            'fields': ('email', 'user_name', 'password1', 'password2', 'is_staff', 'is_admin', 'is_active')
        })
    )


admin.site.register(UserManager, UserAdminConfig)

from django.db.models import CharField, EmailField, DateTimeField
from django.db import models
from django.contrib.auth.models import AbstractBaseUser, BaseUserManager, PermissionsMixin

# Create your models here.
class CustomUserManager(BaseUserManager):
    def create_user(self, email, user_name, password=None, **other_fields):
        if not email:
            raise ValueError('You must provide an email adress')

        email = self.normalize_email(email)
        user = self.model(email=email, user_name=user_name, **other_fields)
        user.set_password(password)
        user.save()
        return user

    def create_superuser(self, email, user_name, password=None, **other_fields):
        other_fields.setdefault('is_staff', True)
        other_fields.setdefault('is_admin', True)
        other_fields.setdefault('is_active', True)

        if other_fields.get('is_staff') is not True:
            raise ValueError('Superuser must be assigned to is_staff=True.')
        if other_fields.get('is_admin') is not True:
            raise ValueError('Superuser must be assigned to is_admin=True.')

        user = self.create_user(email=email, user_name=user_name, password=password, **other_fields)
        user.save()
        return user


class UserManager(AbstractBaseUser, PermissionsMixin):
    email: EmailField = models.EmailField(unique=True, max_length=255)
    user_name: CharField = models.CharField(unique=True, max_length=150)
    registration_date: DateTimeField = models.DateTimeField("Registration Date", auto_now_add=True)

    is_staff = models.BooleanField(default=False)
    is_admin = models.BooleanField(default=False)
    is_active = models.BooleanField(default=True)

    objects: CustomUserManager = CustomUserManager()

    USERNAME_FIELD: str = "email"
    REQUIRED_FIELDS = ['user_name']

    def __str__(self):
       return f"{self.email} {self.user_name} {self.registration_date} {self.is_staff} {self.is_admin} {self.is_active}"
def has_perm(self, perm, obj=None):
        """Does the user have a specific permission?"""
# Simplest possible answer: Yes, always
return True
def has_module_perms(self, app_label):
        """Does the user have permissions to view the app `app_label`?"""
# Simplest possible answer: Yes, always
return True