src/vs/base/browser/ui/tree/objectTreeModel.ts/ObjectTreeModel/getNode
class ObjectTreeModel:	getNode(element: T | null = null): ITreeNode<T | null, TFilterData> {
		if (element === null) {
			return this.model.getNode(this.model.rootRef);
		}

		const node = this.nodes.get(element);

		if (!node) {
			throw new TreeError(this.user, `Tree element not found: ${element}`);
		}

		return node;
	}