SECTION 7A. Appraisal as pre-requisite to payment of damages

An award of damages made pursuant to section six or section seven shall not be made until at least one appraisal has been made in accordance with section twelve on behalf of the taking authority and filed therewith; unless all persons entitled to damages by reason of the taking shall have made a prior written request of the taking authority that the taking be made without awaiting such appraisal and filing, in which event the taking authority may award only nominal damages at the time of adoption of the order but shall, within four months after the taking and after such appraisal is made and filed, amend the award of damages to reflect the damages sustained, and shall immediately after such amendment given written notice thereof to the same persons and in the same manner of service specified by section seven C and, notwithstanding any contrary provision of law, any interest either on damages or on the excess of any payment or deposit made by the taking authority over damages subsequently assessed shall run only from the date of such amendment or the expiration of such four months, whichever is earlier. Notwithstanding the foregoing, no appraisal shall be made by the taking authority if all persons entitled to damages by reason of such taking waive, in writing, their right to any damages.