Finding job owner of a SQL Agent job

I want to find all the jobs which are created by anyone other than sa.

I'm using below query:

select s.name,l.name
from  msdb..sysjobs s 
      left join master.sys.syslogins l on s.owner_sid = l.sid

But owner name comes as null for users who are not part of server log in. Will the name or user id will be stored in any sys tables?