No contract, agreement, or other obligation, involving the expenditure of money out of appropriations made by the commission, shall be entered into, nor shall any order for such expenditure be valid unless the director of finance shall first certify to the commission that the money required for such contract, agreement or obligation is in the treasury to the credit of the appropriation from which it is to be drawn, and that it is otherwise unencumbered. The certificate of the director of finance shall be filed and made a matter of record in his office, and the sum so certified as being in the treasury shall not thereafter be considered unencumbered until the city is discharged from the contract, agreement, or obligation. All unencumbered moneys actually in the treasury to the credit of the appropriation from which an obligation is to be paid, and all moneys applicable to its payment which, before the maturity thereof, are unanticipated to come into the treasury to the credit of such appropriation shall, for the purpose of such certificate, be deemed in the treasury to the credit of the appropriation from which the obligation is to be paid.