Make PARENT field values in search nodes optional (or default to no filter)

Explain the problem as you see it

If I refer to a PARENT field in a search, if that field is empty, the search just doesn't work. This is especially problematic if i'm referring to multiple fields.

Why is this a problem for you?

I want to build a user-friendly data filtering experience, where the filtering options and presentation are defined by me.

Suggest a solution

(see title)