Paginate relations returns null

Is there anyway we can get relationship data with pagination? If I use 'paginate', all relationship data is null.

ForumDiscussion Model

public function user()
  {
    return $this->belongsTo('App\Models\User', 'user_id', 'id')->select(['username']);
  }

Controller

ForumDiscussion::->where('status', 'active')
                            ->with(['user'])->paginate(50);

return relation 'user' null

If I do

ForumDiscussion::->where('status', 'active')
                            ->with(['user'])->get();

relation 'user' has data