Value assigned to locals is not accepted.

LocalsNotAnObject: locals can only be assigned to an object. Other values like numbers, strings, etc. are not accepted.

What went wrong?

Thrown in development mode when locals is overwritten with something that is not an object

For example:

import {defineMiddleware} from "astro:middleware";
export const onRequest = defineMiddleware((context, next) => {
  context.locals = 1541;
  return next();
});