Most of the "optional" method parameters in the BaseClasses API were removed and replaced with overloaded methods. This includes the GetList and DrillDown methods in the Data Access Layer classes.
Customizations in existing applications that override a method with optional parameter(s) need to be manually migrated to use a new method signature.
Customizations in existing applications that call a method with optional parameter(s) should continue to function normally because of the method overloading.
Version 2.0 Application Migration