Deleting an Account Clears the Donor Lookup on Gift Transaction but Is Blocked on Gift Commitment in Nonprofit Cloud

When an Account is referenced by a Gift Commitment, attempting to delete the Account is blocked with the error:

This account is referenced on gift commitments and can't be deleted.

When an Account is referenced only by a Gift Transaction (through the Donor lookup, DonorId), the Account deletes successfully and the Gift Transaction is retained with its Donor lookup cleared, leaving what appears to be an orphaned transaction.

Root cause:

1. On Gift Commitment, the Donor field (DonorId, a lookup to Account) is required. On Gift Transaction, the Donor field (DonorId, a lookup to Account) is optional (nillable).
2. Salesforce lets you configure one of three delete behaviors for a lookup relationship only when the lookup field is optional: clear the field value (default), block deletion of the referenced record, or cascade-delete (custom-to-custom only).
3. Gift Transaction (optional Donor) uses the default "clear the value" behavior, so deleting the Account empties DonorId and keeps the transaction.
4. Gift Commitment (required Donor) cannot have its value cleared, so the platform blocks the Account deletion to preserve referential integrity, producing the error above.

The two objects are not behaving inconsistently; the same lookup-delete rule is applied consistently to a required field versus an optional one. Field definitions were confirmed against the customer org (API v62): GiftTransaction.DonorId nillable = true, GiftCommitment.DonorId nillable = false, both with cascadeDelete = false and restrictedDelete = false. No custom triggers, flows, or validation rules are involved.