DateTimeField with auto_now_add and default is inconsistent/broken

[Norbert Preining]

I wanted to update a model by adding a field

created_at = models.DateTimeField(auto_now_add=True)

But when I wanted to create migrations I got:

$ python manage.py makemigrations users
It is impossible to add the field 'created_at' with 'auto_now_add=True' to customuser without providing a default. This is because the database needs something to populate existing rows.
 1) Provide a one-off default now which will be set on all existing rows
 2) Quit and manually define a default value in models.py.
Select an option: 2

Ok, according to this, I added a default as in

created_at = models.DateTimeField(auto_now_add=True, default=datetime.now)

but creating migrations still complain:

$ python manage.py makemigrations users
SystemCheckError: System check identified some issues:

ERRORS:
users.CustomUser.created_at: (fields.E160) The options auto_now, auto_now_add, and default are mutually exclusive. Only one of these options may be present.

That means, according to the message from manage.py:

• auto_now, auto_now_add, and default are mutually exclusive
• but at the same time, I need to add a default for auto_now_add to be added

I am puzzled

[Norbert Preining]

What works is providing a one-off value by selection 1 in the first case.

[Norbert Preining]

Closing with invalid