Error Scan error on column index 3, name \"short_desc\": converting NULL to string is unsupported

[aselmagzhanova]

Errors in exporter logs:
ts=2025-08-25T13:38:29.358Z caller=postgres_exporter.go:714 level=error err="error retrieving settings: Error retrieving rows on "localhost:5432": pg sql: Scan error on column index 3, name "short_desc": converting NULL to string is unsupported"

Postgres Pro Enterprise 16.6 has null values for these parameters:
replan_enable
replan_show_signature

Please fix pg_settings query.