Hi currently i'm creating a plugins to make a GUI on the Tool Cupboard Inventory but my Gui won't work it say in console "AddUI: Unknown Parent for 'CupboardOverlay': Shield" This is my code:

[ChatCommand("testUI")]
        void UI_Handler(BasePlayer player) {
            CuiElementContainer container = new CuiElementContainer();

            var panel = container.Add(new CuiPanel {

                Image = {
                    Color = "0.1 0.1 0.1 1"
                },
                RectTransform = {
                    AnchorMin = "0.1 0.95",
                    AnchorMax = "0.9 1"
                },
                CursorEnabled = true
            }, "Shield", "CupboardOverlay");

            var button = container.Add(new CuiButton {
                Button = {
                    Command = "say clicked"
                },

                RectTransform = {
                    AnchorMin = "0.4 0",
                    AnchorMax = "0.7 1"
                },
                Text = {
                    Text = "Buy Shield",
                    FontSize = 15
                }
            }, panel);

            CuiHelper.AddUi(player, container);
        }​

According to the error, it means that "Shield" is not a valid parent, as in it doesn't exist in Rust.