A public body need not disclose a bid or proposal to enter into a contract or agreement "until the time for the public opening of bids or proposals, or if a public opening is not to be conducted, until the time for the receipt of bids or proposals has expired." Mich. Comp. Laws Ann. § 15.243(1)(i); see also Nicita v. City of Detroit, 194 Mich. App. 657, 487 N.W.2d 814, 819 (1992) (exemption applies only to a competitive bidding process where bids are solicited but not to unsolicited bids).