After the Board of Review has completed its review of the assessment roll, and on or before the first Monday in April in each year, a majority of its members shall endorse and sign a statement to the effect that the same is the assessment roll of the city for the year in which it has been prepared. The omission of such endorsement shall not affect the validity of such roll. Upon the completion of said roll and from and after midnight following the last day of the meeting of the Board of Review, the same shall be the assessment roll of the city for city taxes on real and personal property that may be authorized by law and under the provisions of this Charter and shall be conclusively presumed by all courts and tribunals to be valid and shall not be set aside except for causes set forth in the general laws of the state.