Subject to the limitations in this subtitle, an officer or unit of the State government may spend an appropriation for a program of the officer or unit in accordance with the current appropriation. Except as provided in subsection (c) of this section, whenever an officer or a unit of the State government spends any part of an appropriation, the officer or unit promptly shall send the bill to the Comptroller for payment. Subject to the limitations in this subtitle, the Comptroller, the Chief Deputy Comptroller, or a deputy comptroller may issue a warrant for payment of the bill. The Comptroller shall exempt an officer or unit of the State government from the requirements of subsection (b) of this section if the Comptroller determines that the exemption would be in the public interest. Subject to the limitations in this subtitle, the Comptroller, the Chief Deputy Comptroller, or a deputy comptroller may issue warrants from time to time to provide the officer or unit with the working cash that the Comptroller finds necessary. The Comptroller shall keep a record that shows each exemption, each amount advanced to an officer or unit, and the reasons for each exemption. The record shall be kept in the Office of the Comptroller and shall be open to public inspection. An officer or unit shall send to the Comptroller the voucher or a copy of the voucher for each expenditure made from an advance under this subsection.