nullable but not null
When working on backend applications, especially those with evolving database schemas, it’s common to see a recurring pattern: A new field is added to a model. To avoid locking the table during the migration, the field is added as nullable. The application logic is updated to start filling in this field. A backfill job runs to populate the existing records. The field is left as nullable. People often forget the final step which is updating the schema to make the field non-nullable once the dat