Neither Council nor any office, department or agency shall, during any budget year, expend or contract to expend any money or incur any liability, or enter into any contract which by its terms involves the expenditure of money, for any purpose, in excess of the amount appropriated for the general budget classification of such expenditure. Any contract, verbal or written, made in violation of this section shall be null and void. Any officer or employee of the City who shall violate this section shall, in addition to any penalties imposed by ordinance or by general law, be removed from his office or employment. Nothing in this section contained, however, shall prevent the making of contracts or the spending of money for capital improvements to be financed in whole or in part by the issuance of bonds, nor the making of contracts of lease or for services for a period exceeding the budget year in which such contract is made, when such contract is permitted by law and funds have been budgeted for payments required by such contract during the current budget year.