Why are 'child' and 'container' always undefined in JsonNode?

[534254884]

export interface JsonNode<View = unknown> extends Identifiable {
name(): string;
view(): View;
children(callback: (node: JsonNode) => void): void;
child?(): JsonNode | undefined;
container(): JsonNode | undefined;
api: undefined | unknown;
}

[streamich]

They are not always undefined. I think they are defined in val and vec nodes.