problem in form_validation using is_callable(), cannot passing data from controller

I think there is no problem with model_joins :: user_campaign. but I have updated my post.

There is a problem because user_campaign is not returning an object. This will be the case when CI_DB_result::row() returns null. It returns null when there are no records returned by the query.

why does it not return object values? instead returns a null value? and how do I overcome that using the is_callable() method?

I tried the callback method before using a query from user_campaign and it worked well without any problems.