Section 506(a) of the Bankruptcy Code provides that a creditor’s claim is a “secured claim to the extent of the value of such creditor’s interest in the estate’s interest in such property”—that is, it is a secured claim for an amount equal to the present value of the collateral—and is an “unsecured claim” for the remainder. Section 506(d) provides that, “[t]o the extent that a lien secures a claim against the debtor that is not an allowed secured claim, such lien is void.”