because user code should never throw NullPointerException. Also made trying to add a child to itself an error instead of a no-op. Attempting to do something like guiNode.attachChild(guiNode) will now throw an IllegalArgumentException.
because user code should never throw NullPointerException. Also made trying to add a child to itself an error instead of a no-op. Attempting to do something like guiNode.attachChild(guiNode) will now throw an IllegalArgumentException.