i use jiglib to create this starget, i try to make it lookat camera but not success, therefore i made a planegeometry call targetex, and make this jiglib cube rotate by following planegeometry’s orientation, this is not the right way, it work but with error massage, can anyone pls help me solve this problem ?   

starget = physics.createCube(stargetmat, 500, 500, 0.01);

targetex = new Mesh(new PlaneGeometry(500, 500, 1, 1, false, false), Mat2);
 
targetex.lookAt(new Vector3D(0, 400, 1977), Vector3D.Y_AXIS);

starget.rotationX = targetex.eulers.x;
starget.rotationY = targetex.eulers.y;
starget.rotationZ = targetex.eulers.z;

Error: Parameter child cannot be null.
at away3d.containers::ObjectContainer3D/addChild()
at away3d.containers::Scene3D/addChild()
at bullet()

sir, what this mean ?