The legacy of a credit against a third person or of the remission or release of a debt of the legatee shall be effective only as regards that part of the credit or debt existing at the time of the death of the testator.
In the first case, the estate shall comply with the legacy by assigning to the legatee all rights of action it may have against the debtor. In the second case, by giving the legatee an acquittance, should he request one.
In both cases, the legacy shall comprise all interests on the credit or debt which may be due the testator at the time of his death. (870a)