// 1. Create table and procedure and fill table with values.
begin
    declare @id integer;

    if exists(select 1 from systable where table_name = '_test_nulls') then
        drop table _test_nulls
    end if;

    create table _test_nulls (
        id integer primary key default autoincrement,
        code varchar(60) null
    );

    create unique index idx_code ON _test_nulls(code);

    if exists(select 1 from sysprocedure where proc_name = '_test_nulls') then
        drop procedure _test_nulls
    end if;

    create procedure _test_nulls()
    result(id integer)
    begin
        declare @id integer;
        declare @code varchar(60);
        select min(id) into @id from _test_nulls where code = @code;
        select @id /* if this row is ommitted (and the row above is without 'into @id')
                      then we have different behavior but still incorrect */
    end;

    insert into _test_nulls (code) values (null);
    insert into _test_nulls (code) values (null);
    insert into _test_nulls (code) values (null);
    /* if this last row is ommitted
       then we have different behavior but still incorrect */
    commit;
end

// 2. A few queries from the procedure that was created above.
begin
    declare @id integer;
    select id into @id from _test_nulls();
    message string('1. ', if @id is null then 'NULL' else 'NOT NULL' endif) to client;
    select id into @id from _test_nulls();
    message string('2. ', if @id is null then 'NULL' else 'NOT NULL' endif) to client;
    select id into @id from _test_nulls();
    message string('3. ', if @id is null then 'NULL' else 'NOT NULL' endif) to client;
    select id into @id from _test_nulls();
    message string('4. ', if @id is null then 'NULL' else 'NOT NULL' endif) to client;
end