with t(a,b) as (select * from table(ku$_objnumpairlist(ku$_objnumpair(1,null))))
select
       json_object(
         KEY 'a' VALUE a,
         KEY 'b' VALUE b absent on null
       ) c2,
       json_object(
         KEY 'a' VALUE a+0,
         KEY 'b' VALUE b null on null
       ) c1,
       json_object(
         KEY 'a' VALUE a+0+0,
         KEY 'b' VALUE b absent on null
       ) c3
from  t;

C2                   C1                   C3
-------------------- -------------------- --------------------
{"a":1}              {"a":1,"b":null}     {"a":1}