bug(thesis): null=True on CharField/TextField creates dual empty representations

[thejoeejoee]

Description

In django/apps/thesis/models/thesis.py, registration_number (CharField) and abstract (TextField) use null=True, and in django/apps/attachment/models/attachment.py, file_path (CharField) also uses null=True.

This creates two possible representations of "empty" in the database: None and '' (empty string). Django's convention for string-based fields is to use blank=True only and store empty values as '', avoiding the ambiguity.

Severity

Medium — data inconsistency, requires OR filters to check for empty values.

Location

• django/apps/thesis/models/thesis.py — registration_number, abstract
• django/apps/attachment/models/attachment.py — file_path

Fix

Remove null=True from these string fields and add a data migration to convert existing NULL values to ''.