Querying SSISB parameters - get_parameter_values always returns null?

There is a stored procedure that comes with SSISDB - get_parameter_values(). This retrieves project and package scope parameter information. However, there are two issue with this which I wonder if anyone knows anything about -

1. the @package_name parameter to this SP is supposed to accept NULL and then return information on all packages. It doesn't - it just complains that the param is null.
2. The returned "parameter_value" column is almost always NULL and rarely reflects any value set when looking through the IS catalog in SSDT?