Django-filer fails to create the model. What can be done?

Question

Django

makemigrations throws an error

super(FilerFileField, self).__init__(**kwargs)
TypeError: __init__() missing 1 required positional argument: 'on_delete'

Here is the model:

from django.db import models
from filer.fields.image import FilerImageField 

class Book(models.Model):
    title = models.CharField(max_length=200)
    cover = FilerImageField(null=True, blank=True, related_name="book_covers")

Answer 1

Django docs