Privacy setting to enable online_presence?

We're developing an application which need to get user's friends' online presence. I'm already getting everybody's presence but some of them returns null value. I googled it and some say that it's a privacy setting for each user.

I looked at my facebook test account's privacy settings and the only content is this:

Your status, photos, and posts

Bio and favorite quotations

Family and relationships

Photos and videos you're tagged in

Religious and political vi开发者_Go百科ews

Birthday Permission to comment on your posts

Places you check in to Contact information

Everything is set to public for everybody but then I still its online_presence returns NULL value. Where can I find that setting to enable online_presence permission? Thanks!

If you are using FQL, then the required permissions are 'user_online_presence', 'friends_online_presence'. Alternatively, with XMPP, it is 'xmpp_login'.