Even if MariaDB treats catalogs and schemas identically, being able to define all three values seems like a reasonable expectation. In information_schema.tables, all tables have the catalog set to def so one would expect to be able to define the exact table to be inspected using the information in information_schema.

I would suggest a backwards compatible change: if the given catalog is def or if the catalog is identical to the schema, take the catalog from the schema argument instead.