Whenever heretofore any board of school directors of any school district shall have advertised for and let bids for the construction and erection of any school building or an addition to an existing school building, and such building or addition has been actually constructed or erected and completed by the contractor or contractors and is available for use by the school district, and where any such contract or proceedings in connection therewith do not evidence any fraud or conspiracy to violate any of the laws of the Commonwealth relating to such contracts, then in such cases any such contract and all proceedings of the board of school directors in connection therewith are hereby confirmed, ratified, and made valid, and the board of school directors is hereby authorized to accept such building or addition to an existing school building on behalf of the school district, to use the same for public school purposes, and to pay to the contractor or contractors the amount due thereon under the terms of the contract, from the funds of the school district raised by taxation, notwithstanding the fact that such contract or contracts were legally null and void for the reason that the bids for the building or addition were not in accordance with the advertisement inviting bids, or that the bidders did not bid on the same basis as to the time for the completion of the contract, or because certain changes were made verbally in the plans and specifications and in the bidding as advertised by the secretary of the board of school directors when he handed out the specifications, which changes were never advertised as required by law, or because after the contract was awarded to the contractor the board of school directors agreed to pay the surety board which was taken to guarantee the faithful compliance by the contractor or contractors with the terms of their contracts, or because the contract was executed in violation of the provisions of the laws of the Commonwealth, or because the advertisement did not fix the time at which the building or annex was to be completed, or for any other reason whatsoever.