MoveAlongJointPath joint-list

I was wondering if it is allowed to send only a subset of joints in the MoveAlongJointPath path? Ideally, the remaining joints will be kept at their initial values.
Or do we need to send values for all the joints, even when some are being kept static?

Also, is there a quick way to stop the robot instead of having to send another MoveAlongJointPath with a pose corresponding to the current pose?

Thanks!

So, it seems sending a subset of joints works.
It would be cool if the robot just stops if the joint-list is empty.