Setting null = false on m2m fields causes migration to fail

[intigratech]

I have a m2m field as follows:

class Contact(RootModel):
categories = fields.ManyToManyField('core.ContactCategory', related_name='contacts', through='fkcontactcategory',
description="Categories", on_delete=fields.SET_NULL)

I set null=False on the field.
categories = fields.ManyToManyField('core.ContactCategory', related_name='contacts', null=False, through='fkcontactcategory', description="Categories", on_delete=fields.SET_NULL)

When performing the migration using command.migrate(app_name) I run into an error:
'bool' object is not subscriptable

Any help would be appreciated.