Det ser ud til, at du har tilføjet null=True
efter oprettet migrationsfil. Fordi venue_city
er ikke et nullbart felt i din migreringsfil
Følg disse trin.
1) Drop venue_city & venue_country from your local table
3) Delete all the migration files you created for these `CharField to a ForeignKey` change
4) execute `python manage.py makemigrations`
5) execute 'python manage.py migrate'
Det burde virke