in _validate_username AttributeError: 'Manager' object has no attribute 'get_by_natural_key' error

models.py:

from django.db import models
from django.contrib.auth.models import AbstractBaseUser, PermissionsMixin
from .managers import UserAccountManager
        
class UserAccount(AbstractBaseUser, PermissionsMixin):
    email = models.EmailField(
        max_length=255,
        unique=True,
        # null=False,
        # blank=False,
        verbose_name="email",
    )
    name = models.CharField(max_length=255)
            
    is_active=models.BooleanField(
        default=True,
        )
    is_staff=models.BooleanField(
        default=False,
        )
    is_admin=models.BooleanField(
        default=False,
        )
    created_at=models.DateTimeField(auto_now_add=True)
        
    objects: UserAccountManager()
        
    USERNAME_FIELD = 'email'
    REQUIRED_FIELDS = ['name']
           
    def __str__(self):
       return self.email
    

managers.py:

from django.contrib.auth.models import BaseUserManager
              
                
class UserAccountManager(BaseUserManager):
    def create_user(self, email, name, password=None):
   """Creates and saves a User with the given email, name and password."""
        if not email:
            raise ValueError('Users must have an email address')
                        
        email=self.normalize_email(email)
        email = email.lower()
        
        user = self.model(
            email=email,
            name=name
        )
       
        user.set_password(password)
        user.save(using=self._db)
        return user
        
    def create_admin(self, email, name, password=None):
        """
        Creates and saves a superuser with the given email, name and password.
        """
        user = self.create_user(email, name, password)
        user.is_admin = True
        user.is_staff = True
        user.save(using=self._db)
        return user
            
    def create_superuser(self, email, name, password=None):
        """
        Creates and saves a superuser with the given email, name and password.
        """
        user = self.create_user(email, name, password)
        user.is_staff = True
        user.is_admin = True
        user.is_superuser = True
        user.save(using=self._db)
        return user