How to assign an empty value to an object attribute in Django Admin Interface?

I’m designing an eBay-like website. My project has several models, one of which, namely "Listing", represents all existing products:

class Listing(models.Model):
    title = models.CharField(max_length=64)
    description = models.CharField(max_length=512)
    category = models.CharField(max_length=64)
    image_url = models.URLField()
    owner = models.ForeignKey(User, on_delete=models.CASCADE, related_name="created_listings")
    is_active = models.BooleanField(default=True)
    winner = models.ForeignKey(User, on_delete=models.CASCADE, related_name="won_listings", null=True)

I need the winner attribute to be able to equal an empty value. But when I try to assign it an empty value in Django Admin Interface, I get an error:

How can I solve this problem? Thank you in advance!

>Solution :

You use blank=True ^[Django-doc] to make the field non-required:

class Listing(models.Model):
    # …
    winner = models.ForeignKey(
        User,
        on_delete=models.CASCADE,
        related_name="won_listings",
        null=True,
        blank=True,
    )

Note: It is normally better to make use of the settings.AUTH_USER_MODEL ^[Django-doc] to refer to the user model, than to use the User model ^[Django-doc] directly. For more information you can see the referencing the User model section of the documentation.