Use default value instead of inserted null

I have a table definition in Postgres that use now() for timestamp and current_user() for auditing. date_created date NULL DEFAULT now(), edited_by varchar NULL DEFAULT "current_user"(), The problem is that the server produces queries with explicit null values if not given other instructions. I have no way of changing the query being sent from the server to pg. INSERT INTO test_table (notes, date, edited_by) VALUES('test', null, null); Is there a way to still use these default values somehow? Or is the solution to write a trigger function to solve it?