The middleware didn't return a response or call next.

MiddlewareNoDataOrNextCalled: The middleware needs to either return a Response object or call the next function.

What went wrong?

Section titled What went wrong?

Thrown when the middleware does not return any data or call the next function.

For example:

import {defineMiddleware} from "astro:middleware";
export const onRequest = defineMiddleware((context, _) => {
  // doesn't return anything or call `next`
  context.locals.someData = false;
});