The plpgsql proc has "object_type" as the defined parameter:
see content-type.sql
select define_function_args('content_type__is_content_type','object_type');
This is the same for oracle.
I am not sure what problem you are trying to fix here. If it did not work, what error message or unexpected behavior did you see?
The code in application-data-links procs refers to a parameter that is wrong. It seems like calling the procedure correctly according to the plpgsql function defition is the right fix here.
Am I missing something?