title: TypeError: create_superuser() got an unexpected keyword argument 'email'
body: <p>I need to create custom user model because I need to have one additional field called role. If the role is provided, it should be assigned to the user model otherwise provide agent as role in user model. I inherited the <code>AbstractUser</code>. This way when creating the user, first the password is saved as plain text and another is user cannot login it says unable to login. So i tried the below way as in docs but the problem is i don't need the email part so i excluded it and used just username and password but getting error like <code>TypeError: create_superuser() got an unexpected keyword argument 'email'</code></p>
  
  <pre><code>class UserManager(BaseUserManager):
          def create_user(self, username, password=None):
              """
              Creates and saves a User with the given username, date of
              birth and password.
              """
              if not username:
                  raise ValueError('Users must have an username')
              user = self.model(username=username)
              user.set_password(password)
              user.save(using=self._db)
              return user
  
      def create_superuser(self, username, password):
          """
          Creates and saves a superuser with the given username and password.
          """
          user = self.create_user(
              username=username,
              password=password,
          )
          user.is_admin = True
          user.save(using=self._db)
          return user
  
  
  class Role(models.Model):
  
      ROLE_CHOICES = (
          ('agent', 'Agent'),
          ('agency', 'Agency'),
          ('manufacturer', 'Manufacturer'),
      )
      role = models.CharField(max_length=15, choices=ROLE_CHOICES)
  
      def __str__(self):
          return self.role
  
  
  class User(AbstractUser):
  
      role = models.ForeignKey(
          Role,
          on_delete=models.CASCADE,
          blank=True,
          null=True,
      )
  
      objects = UserManager()
  
      def __str__(self):
          return self.username
  
  
  @receiver(models.signals.post_save, sender=User)
  def add_role_to_user(sender, instance, **kwargs):
      print('instance in add role', instance)
      if kwargs.get('created'):
          try:
              role = Role.objects.get(user=instance)
              print('role', role)
          except Role.DoesNotExist:
              Role.objects.create(role="agent")
          try:
              token = Token.objects.get(user=instance)
              print('token', token)
          except Token.DoesNotExist:
              Token.objects.create(user=instance)
  </code></pre>