I am trying to add follow/unfollow functionality to my app. when I add populate methods in userById it stops showing user info on profile pages. what can I do?

 exports.userById = (req, res, next, id)=>{
 User.findById(id)
 .populate('following', '_id username')
 .populate('followers', '_id username')

 .exec((err,user)=>{
     if(err || !user){
        return res.status(400).json({
             error: "user not found"
         })
     }
     req.profile=user 
     next()
 })

}