SQL upsert with GUI should allow null values in the filter

I have a form that has some optional fields. When they aren't filled in I want those fields to be considered NULL in the database. When trying to "Update a record, or create a new record if it doesn't exist" and using the GUI, it would be ideal to have an option that checks for
(field IS NULL OR field={{input.value}}
When I simply use the = operator then a new row gets created every time that I leave an optional field blank because field = NULL evaluates to false.