Android : Can't access ParseObject from include

I used the same method with AnyPic, and i create a Class in Parse called : Activities.

Activities :

• fromUser = Pointer : User


• toUser = Pointer : User


• toMedia = Pointer : Media


• toPost = Pointer : Activities


• type = Number

I put a pointer of Activity so that i can like comment for example, or i can repost an already existing post.

But when i'm trying to access it, i can't. Here's the query :

ParseQuery<ActivityObject> query = ParseQuery
            .getQuery(ActivityObject.class);
    query.include(ActivityHelper.FIELD_FROM_USER);
    query.include(ActivityHelper.FIELD_TO_MEDIA);
    query.include(ActivityHelper.FIELD_TO_POST);
    query.include(ActivityHelper.FIELD_TO_USER);
    query.whereEqualTo(ActivityHelper.FIELD_FROM_USER,
            ParseUser.getCurrentUser());
    query.addDescendingOrder(ActivityHelper.CREATED);
    query.findInBackground(new FindCallback<ActivityObject>() {

        @Override
        public void done(List<ActivityObject> ac, ParseException e) {
            // TODO Auto-generated method stub

            if (e == null) {
                activities = ac;
                adapter = new ActivityAdapter(context, activities);
                lv.setAdapter(adapter);
                lv.setOnItemClickListener(listener);
            }
        }
    });

But in my getView method, i can't access fromUser nor the Media, but getPost() works anyway, with this :

str = str + " liked "
                + activity.getPost().getFromUser().getUsername() + "'s "
                + getMediaType(activity.getPost().getMedia().getType());
        if (activity.getPost().getExtra() != null) {
            str = str + " : " + activity.getPost().getExtra();
        }

The error i got is :

ParseObject has no data for this key, Call fetchIfNeeded() to get data.