Laravel: Writing right nested conditional queries (code reduction)

Ok, so this is my code.

What it does is check some worker's fields to find posible duplicates (I know this fields should be unique, but I can't do so much about that). So for instance if the field $credential_no is set, it checks in DB, but if it's null, it doesn't because I don't want all the records that has null in that field.

The thing here, is that I need to check if at least some of that inputs ($credential_no || $ssn || $passport_no || $birthdate) are defined because if not, the query will returns all the workers, cause are none where condition, and I want results only if there's a match.

Also, by trying, I realice that I can use where and orWhere indistinctly, am I wrong? because if not I must use something like this:

My question is how can I make this thing better, how can I reduce this messy code, or there is no way in laravel to do this kind of thing?

via Chebli Mohamed