Arkit & hand pose detection

On Arkit project, in funtion -
func session(_ session: ARSession, didUpdate frame: ARFrame)

I tried to get -
guard let observation = handPoseRequest.results?.first as? VNRecognizedPointsObservation else { return }

and get -
let thumb = try! observation.recognizedPoints(forGroupKey: .handLandmarkRegionKeyThumb)

segmentation fault 11 pop up.

Is this a bug ? or did I made any mistake?