src/vs/workbench/browser/parts/views/treeView.ts/CustomTreeViewDragAndDrop/getDragURI
class CustomTreeViewDragAndDrop:	getDragURI(element: ITreeItem): string | null {
		if (!this.dndController) {
			return null;
		}
		return element.resourceUri ? URI.revive(element.resourceUri).toString() : element.handle;
	}