Error #1009

1

Any ideas?

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at jumpingjack_fla::MainTimeline/frame1()[jumpingjack_fla.MainTimeline::frame1:4]
Debug session terminated.

import fl.ik.*;
var body : IKArmature = IKManager.getArmatureAt(0);
var leftHand : IKBone = body.getBoneByName("LeftHand");
var leftHandJoint :IKJoint = leftHand.tailJoint;
var moveLeft : IKMover = new IKMover(leftHandJoint, leftHandJoint.position);
if(leftHandJoint.position.y != 86) {
 leftHandJoint.position.y = 86;
} else if(leftHandJoint.position.y == 86) {
 leftHandJoint.position.y = 100;
}