With as not working, PostgreSQL

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--PostgreSQL 9.6
--'\\' is a delimiter

CREATE TABLE Domain (
	id int4 NOT NULL,
	name varchar NULL,
	isdefault bool NULL
);

INSERT INTO Domain
(id, name, isdefault)
VALUES(1, 'robert', false);

INSERT INTO Domain
(id, name, isdefault)
VALUES(2, 'ant', true);

INSERT INTO Domain
(id, name, isdefault)
VALUES(3, 'gei', false);

select * from Domain;

CREATE OR REPLACE FUNCTION myTestProcedure(namevalue character varying)
 RETURNS TABLE(id integer, name character varying, isdefault boolean)
 LANGUAGE plpgsql
AS $function$
  BEGIN
    with temporal_result as (
      SELECT
        Domain.id,
        Domain.name,
        Domain.isdefault
      FROM Domain
      where lower(Domain.name) like namevalue
    )
    IF EXISTS(temporal_result)
    THEN
      RETURN QUERY SELECT * from temporal_result;
    ELSE
     RETURN QUERY SELECT
        Domain.id,
        Domain.name,
        Domain.isdefault
      FROM Domain
      where Domain.isdefault = true;
    END IF;   
  END
$function$;

-- should return robert
select * from myTestProcedure('robert');

-- should return ant, the default one
select * from myTestProcedure('roberta');


Absolute service time: 0,52 sec, absolute service time: 0,51 sec