Fetching data with either null and value on where conditions are very tricky. Even if you are using straight Where and OrWhereNotNull condition then for every rows you will fetch both items ignoring other where conditions if applied. For example if you have more where conditions it will mask out those and still return with either null or value items because you used orWhere condition
The best way so far I found is as follows. This works as where (whereIn Or WhereNotNull)
Code::where(function ($query) {
$query->where('to_be_used_by_user_id', '!=' , 2)->orWhereNull('to_be_used_by_user_id');
})->get();