src/vs/workbench/services/extensions/common/rpcProtocol.ts/MessageIO/serializeReplyErr
class MessageIO:	public static serializeReplyErr(req: number, err: any): VSBuffer {
		if (err) {
			return this._serializeReplyErrEror(req, err);
		}
		return this._serializeReplyErrEmpty(req);
	}