如何在不使用用户名字段的情况下在django中创建自定义用户模型？

from django.contrib.auth.models import BaseUserManager

class CustomUserManager(BaseUserManager):
    def create_user(self, email, password=None, **extra_fields):
        if not email:
            raise ValueError('The Email field must be set')
        email = self.normalize_email(email)
        user = self.model(email=email, **extra_fields)
        user.set_password(password)
        user.save(using=self._db)
        return user

    def create_superuser(self, email, password=None, **extra_fields):
        extra_fields.setdefault('is_staff', True)
        extra_fields.setdefault('is_superuser', True)
        return self.create_user(email, password, **extra_fields)

from django.contrib.auth.models import AbstractBaseUser, PermissionsMixin
from django.db import models

class CustomUser(AbstractBaseUser, PermissionsMixin):
    email = models.EmailField(unique=True)
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    is_active = models.BooleanField(default=True)
    is_staff = models.BooleanField(default=False)

    USERNAME_FIELD = 'email'

    objects = CustomUserManager()

    def __str__(self):
        return self.email

AUTH_USER_MODEL = 'your_app.CustomUser'