Exercise 1: null=True vs. blank=True — Possible Solution
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THE DIFFERENCE
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null=True is a database-level setting - it allows the actual SQL column to store NULL. blank=True is a form/admin-level setting - it allows Django's forms and the admin site to accept an empty value for that field without raising a validation error. One controls what the database will store; the other controls what forms will accept as valid input.

WHY expiry_date NEEDS BOTH
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null=True is needed so that a used item's row can genuinely have no expiry date stored at the database level - without it, the database itself would reject an attempt to leave the column empty. blank=True is needed separately so that the admin site or a Django Form doesn't reject an empty expiry date as a validation failure before the data even reaches the database - without it, a user (or the admin) would hit a "this field is required" error even though the database itself would happily store NULL for that field.

WHY THIS WORKS AS AN ANSWER
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It correctly distinguishes the database-level meaning of null=True from the form/validation-level meaning of blank=True, and correctly explains why expiry_date requires both settings independently to actually behave as a genuinely optional field at every layer, not just one.