如何在Django v3中正确编写自定义用户模型和管理器？

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

class CustomUserManager(BaseUserManager):
    def create_user(self, email, password=None, **extra_fields):
        # 创建普通用户
        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):
        # 创建超级用户
        extra_fields.setdefault('is_staff', True)
        extra_fields.setdefault('is_superuser', True)
        return self.create_user(email, password, **extra_fields)

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)

    objects = CustomUserManager()

    USERNAME_FIELD = 'email'
    REQUIRED_FIELDS = ['first_name', 'last_name']

    def get_full_name(self):
        return f'{self.first_name} {self.last_name}'

    def get_short_name(self):
        return self.first_name