fix express.NextFunction

express-serve-static-core/express-serve-static-core.d.ts

@@ -783,8 +783,7 @@ declare module "express-serve-static-core" {
     }
 
     interface NextFunction {
-        (): void;
-        (err: any): void;
+        (err?: any): void;
     }
 
     interface ErrorRequestHandler {

express/express-tests.ts

@@ -68,3 +68,6 @@ app.use((req, res, next) => {
 app.use(router);
 
 app.listen(3000);
+
+const next: express.NextFunction = () => {};
+const nextWithArgument: express.NextFunction = (err: any) => {};