Hi,
I've just been testing the method "rtm.lists.setDefaultList" [1] and it seems that the documentation is wrong.
From the documentation "list_id (Optional) The id of the list to perform an action on", but this field is mandatory.
As expected, if you want to set a list as the default list, you should pass as argument the "list_id".
So, if I'm not wrong, the API documentation at website should be fixed