Asana API: How do I remove a parent from a subtask with the new setParent endpoint -

according asana api documentation should possible remove parent subtask, subtask becomes normal task:

creating subtask same creating normal task, instead of specifying workspace must specify parent task. each task can have single parent , can use setparent endpoint add or remove parent existing task.

however it's not clear me how can remove parent endpoint. i've tried following things body of request

parent=0  

=> 400 bad request {"errors":[{"message":"parent: not id: 0"}]}

null  

=> 400 bad request {"errors":[{"message":"could not parse request data, invalid json"}]}

parent={subtaskid}  

=> 500 error (makes sense can't add subtask parent of itself, shouldn't 500 error think) {"errors":[{"message":"server error","phrase":"14 orange apes run smoothly"}]}

parent= 

=> 400 bad request {"errors":[{"message":"parent: not id: "}]}

is @ possible, , if so, how?

(i work @ asana.) have tried parent=null?