create table testing(num int, dt date, istrue boolean);

insert into testing values (1, '2018-01-01', True);

UPDATE testing SET num = 2, istrue = null AND dt = '2018-01-01';

UPDATE testing SET num = 2, istrue = null WHERE dt = '2018-01-01';

null AND dt = '2018-01-01'

null AND dt = '2018-01-01'

UPDATE
    testing
SET
    num = 2,
    istrue = ( null AND (dt = '2018-01-01') )
;