Using an empty string as the default for a ForeignKey is likely to cause issues since it expects an integer or a valid instance reference. Consider using a proper default value (e.g., None or a valid pk) or handling it via a custom migration data migration.

[pollardld]

          Using an empty string as the default for a ForeignKey is likely to cause issues since it expects an integer or a valid instance reference. Consider using a proper default value (e.g., None or a valid pk) or handling it via a custom migration data migration.

            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='layers.layer'),

Originally posted by @Copilot in #7 (comment)