Unable to access reference object properties on createSchemaCustomization

[AbdallahAbis]

I'm trying to add a custom field to my SanityDocument by using createSchemaCustomization API, the new field will combine a few SanityDocument fields in one, but one of those fields is a reference field and on sanity GROQ it could be accessed like brand->name but on I don't know how to access it on createSchemaCustomization.

My createSchemaCustomization:

exports.createSchemaCustomization = ({ actions, schema }) => {
  actions.createTypes([
    schema.buildObjectType({
      name: "SanityDocument",
      interfaces: ["Node"],
      fields: {
        title: {
          type: "String!",
          resolve: (source) => {
            console.log(source.brand)
            return `${source.model} ${source.brand.name}`
          }
        },
      },
    }),
  ]);
};

This doesn't work, logging source.brand outputs

"brand":{
  "_ref":"brand-36fef2ab-a5a0-472d-ac92-0f14cb9cae6b"
  "_type":"reference"
}