src/vs/editor/common/model/editStack.ts/MultiModelEditStackElement/getMissingModels
class MultiModelEditStackElement:	public getMissingModels(): URI[] {
		const result: URI[] = [];
		for (const editStackElement of this._editStackElementsArr) {
			if (URI.isUri(editStackElement.model)) {
				result.push(editStackElement.model);
			}
		}
		return result;
	}