User profile models with nullable emails cannot use createsuperuser command

[Jonas Dittrich]

We have a custom user model defined, that does not have a natural key and in fact all fields (except pk) may be duplicated. That is because we can have "special" users that do not have an email.

Our model looks like this (minimal user model without a natural key implementation):

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

class UserProfile(PermissionsMixin, models.Model):
    # null=True because certain external users don't have an address
    email = models.EmailField(max_length=255, unique=True, blank=True, null=True, verbose_name="email address")
    password = models.CharField("password", max_length=128)

    @property
    def is_anonymous(self):
        return False

    @property
    def is_authenticated(self):
        return True

    USERNAME_FIELD = "email"
    REQUIRED_FIELDS = ["password"]

Now, using ./manage.py createsuperuser is no longer possible. After entering an email address:

Email address: user@example.com
Traceback (most recent call last):
  File "./manage.py", line 22, in <module>
    main()
  File "./manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File ".../lib/python3.10/site-packages/django/core/management/__init__.py", line 442, in execute_from_command_line
    utility.execute()
  File ".../lib/python3.10/site-packages/django/core/management/__init__.py", line 436, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ".../lib/python3.10/site-packages/django/core/management/base.py", line 413, in run_from_argv
    self.execute(*args, **cmd_options)
  File ".../lib/python3.10/site-packages/django/contrib/auth/management/commands/createsuperuser.py", line 90, in execute
    return super().execute(*args, **options)
  File ".../lib/python3.10/site-packages/django/core/management/base.py", line 459, in execute
    output = self.handle(*args, **options)
  File ".../lib/python3.10/site-packages/django/contrib/auth/management/commands/createsuperuser.py", line 132, in handle
    error_msg = self._validate_username(
  File ".../lib/python3.10/site-packages/django/contrib/auth/management/commands/createsuperuser.py", line 305, in _validate_username
    self.UserModel._default_manager.db_manager(database).get_by_natural_key(
AttributeError: 'Manager' object has no attribute 'get_by_natural_key'

Command._validate_username does check if the username field is unique by looking at the unique flag passed to the field. However, we also set null=True, so our username is not unique in the sense that a get_by_natural_key can be implemented at all.

The create superuser command should either check for a nullable or blank username field in addition to the unique flag, or directly check if the user model has the attribute get_by_natural_key defined.