This verb's callback function code located in :

https://git.automotivelinux.org/apps/agl-service-bluetooth/tree/binding/bluetooth-api.c

line 1003~1028

I investigate it  and found several issues of this function.

To be honest, In this process,  I also refer the code of similar use inside Debian's NetworkManager, which is a popular wifi/bt managerment tool in gnome.

Issues :

 if user specify no adapter or the same adapter with exsiting one, we should just reply with system default adapter and dont need to invoke set_default_adapter() or update DB