Incorrect return type when cloning a TransformNode

Cloning a TransformNode seems to return Nullable<TransformNode> but it seems that clone can never return null, so it should return just TransformNode. Probably this Nullable comes from AbstractMesh which extends TransformNode?

What about throwing if AbstractMesh is cloned instead of returning null?

yeah we need to keep the nullable for children but if you are cloning a transform node you can just use !:

let myClone = transformNode.clone()!;