'resolver not found' with Apollo Server 4 (express) + NextJs + external graphql endpoint
hi there-
I have searched extensively to figure out the right way to 'merge' my custom schema with an external one. It was pretty straightforward in Apollo Server v2 utilizing graphql-tools, and now I can't get around this resolver not found issue (I did read all the other related bugs). Could someone please tell me what I should be using with Apollo Server 4? Is it the "Federation" aspect, or a context pointing to my hasura GraphQL endpoint or ?

this is the code that is failing:
```
const EXTERNAL_ENDPOINT = "http://localhost:8080/v1/graphql";


async function remoteExecutor({ document, variables }) {
    const query = "query dummyQuery { campaigns { id } }";
    const response = await fetch(EXTERNAL_ENDPOINT, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ query, variables })
    })
    return response.json()
  };

const createRemoteSchema = (async () => {
  return {
     schema: await introspectSchema(executor),
     executor: remoteExecutor
  }
}

const setupServer = async() => {
  // make executable schema out of custom resolvers and typedefs

//internal schema containing auth stuff, custom resolvers
  const executableCustomSchema = makeExecutableSchema({
    typeDefs,
    resolvers
  });

// external schema out on heroku (but testing locally)
// I had been using introspectSchema in an early version of apollo-server and graphql-tools
  const externalSchema = await createRemoteSchema();


  const finalSchema = mergeSchemas({
    schemas: [
      executableCustomSchema,
      externalSchema
    ]
  });


  const aServer = new ApolloServer({ finalSchema });

  const { url } = await startStandaloneServer(aServer, {
    listen: { port: 4001 }
  });

// tried returning { aServer} but always the error "Resolver not found" in node_mobules/next/node.js line 366
})();

setupServer();
// and I cannot attach the createHandler function as it says it doesn't exist  :(


export const config = {
  api: {
    bodyParser: false
  }
};

```