BUG #13768: JSONB concat

The following bug has been logged on the website:

Bug reference:      13768
Logged by:          Roman
Email address:      awasarax@yandex.ru
PostgreSQL version: 9.5beta1
Operating system:   Windows (7, Server 2008 r2)
Description:

if "d" is null then return = null
else
return <> null


CREATE OR REPLACE FUNCTION userfunc(jsonb)
  RETURNS jsonb AS
$BODY$
DECLARE
 r jsonb = null;
 d jsonb = null;
BEGIN
 SELECT to_json(users.*) INTO r FROM users WHERE ///////;
 RETURN r||d; -- return null
END;
$BODY$
  LANGUAGE plpgsql VOLATILE;