diff --git a/files/en-us/learn/server-side/django/models/index.html b/files/en-us/learn/server-side/django/models/index.html
index 6db0a7952528851..c7500429b7ce357 100644
--- a/files/en-us/learn/server-side/django/models/index.html
+++ b/files/en-us/learn/server-side/django/models/index.html
@@ -338,7 +338,7 @@
BookInstance model
class BookInstance(models.Model):
"""Model representing a specific copy of a book (i.e. that can be borrowed from the library)."""
id = models.UUIDField(primary_key=True, default=uuid.uuid4, help_text='Unique ID for this particular book across whole library')
- book = models.ForeignKey('Book', on_delete=models.RESTRICT)
+ book = models.ForeignKey('Book', on_delete=models.RESTRICT, null=True)
imprint = models.CharField(max_length=200)
due_back = models.DateField(null=True, blank=True)