Resolve with aliased fields

[JonasDoe]

I'm having problem understanding how to work with aliases. Since the behavior didn't change after upgrading graphql-tools to 9.0.0,I guess it's not a bug but a feature. Can you help me to shed a bit of light on it?
I'm merging a schema like this one. I've added a dummy resolver for event to reduce the complexity of my example request:

const mySchema = mergeSchemas({
    resolverValidationOptions: { requireResolversToMatchSchema: 'ignore' },
    schemas: mySchemas,
    typeDefs: myTypes,
    resolvers: {
      Query: {
        'event': (source, args, context, info) => {
          return {
            introAlias: 'myIntroText',
          };
        },
      },
    },
  });

For this, my query

query {
  event(id: "myEventId") {
    introAlias: intro
  }
}

will fail with "Cannot return null for non-nullable field Event.intro.". (The field is intended to be mandarory.)

I found a hint pointing out that alias resolving won't work for delegateSchema calls, but apparantly I'm not using that in my example event resolver.
I was wondering whether I have to delegate the call defaultMergedResolver manually somehow, but since source is undefined here, calling it won't do anything.

I could try to resolve the aliases manually, of course, based on the information scraped together from the info argument. But I've got the feeling I'm missing something obvious here - do I?

Thanks for any feedback!

[JonasDoe]

Nevermind, I realized I just got tunnel vision. The original call is of course delegated, and my simplified event resolver must not return the the property with the alias name, but with the underlying one. So a transfomation of the outgoing request (just call (node: FieldNode) => ({ ...node, alias: undefined }) for each FieldNode in the visitor pattern) did the trick.