Except as provided in subsection (c) of this section, on receipt of a written complaint, the Board promptly shall: send the complaint to the custodian or applicant identified in the complaint; and request that a response to the complaint be sent to the Board. The custodian or applicant shall file a written response to the complaint within 30 calendar days after receiving the complaint. On request of the Board, the custodian shall provide: if the complaint alleges that the custodian failed to respond to a request for a public record within the time limits established under § 4–203 of this title, a response to the request for the public record; if the complaint alleges that the custodian denied inspection of a public record in violation of this title: a copy of the public record, descriptive index of the public record, or written reason why the record cannot be disclosed, as appropriate; and the provision of law on which the custodian relied in denying inspection of the public record; or if the complaint alleges that the custodian charged an unreasonable fee under § 4–206 of this title, the basis for the fee that was charged. If the complaint alleges that the custodian denied inspection of a public record under § 4–301(a)(2)(ii) of this title, the custodian may not be required to produce the public record for Board review. The Board may request information about the public record from the custodian. On request of the Board, a custodian or an applicant shall provide an affidavit or a statement containing the facts that are at issue in the complaint. The Board shall maintain the confidentiality of any record or information submitted by a custodian or an applicant under this subsection. A custodian may not be civilly or criminally liable under Maryland law for providing or describing a public record to the Board under this subsection. The provision of a record or a description of a record to the Board under this subsection may not be construed as a waiver of any applicable privilege. If a written response or information requested under subsection (b) of this section is not received within 30 calendar days after the request is sent, the Board shall decide the case on the facts before the Board.